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Full text of "Animal life in deserts, a study of the fauna in relation to the environment"

^ 



ANIMAL LIFE IN DESERTS 



ANIMAL LIFE IN 
DESERTS 

A STUDY OF THE FAUNA IN 
RELATION TO THE ENVIRONMENT 



BY 

P. A. BUXTON, M.A. 

FORMERLY FELLOW OF TRINITY COLLEGE, CAMBRIDGE 
MEDICAL ENTOMOLOGIST, GOVERNMENT OF PALESTINE 



ILLUSTRATED 






LONDON 

EDWARD ARNOLD & CO. 

1923 

\^All fights reserved] 






Ql 

\\io 

B^8 



Made and Printed in Great Britain by 
Buder & Tanner, Frame and London 



PREFACE 

Circumstances over which I had no control 
induced me to study the conditions of Ufe in Lower 
Mesopotamia and in North- West Persia for more 
than two years. I had previously seen desert life 
in spring-time during a short visit to Algeria, and 
more recently I have lived in Jerusalem, a city 
which is not indeed in the desert, but within easy 
reach of the deserts of Southern Palestine and of the 
lower end of the Jordan depression. I have endeav- 
oured to summarize my own observations and to 
elucidate their meaning by comparison with what 
has been observed in other deserts. The desert is an 
environment unspoilt by the hand of man, so that 
one can more clearly observe the interaction of 
plant and animal upon each other, and the depen- 
dence of the living creatures upon climate and 
other physical conditions. 

This " oecological " study will, I hope, prove 
interesting to many who delight in natural history, 
but who have never had an opportunity to make 
themselves acquainted with the more formal aspects 
of Zoology. As every reader will discover, the study 
of the animal in relation to its surroundings is beset 
with difficulties ; we are ignorant of certain details 

V 



vi PREFACE 

of the climatology of deserts, and of the life-history 
of the great majority of the smaller animals, and 
there is at present a complete absence of experi- 
mental work upon them. It is partly in order to 
summarize our present knowledge and to draw 
attention to the graver deficiencies in it that this 
book has been written. 

The study of the desert creatures and their 
environment leads one to a very fascinating meet- 
ing-place of several sciences. It can only be 
approached with the help of botanists, meteorol- 
ogists, physicists, and others. My debt to my 
fellow-workers is the greater because the book was 
written in Jerusalem, without access to a good 
library ; I have therefore been forced to rely on the 
kindness and generosity of correspondents, many 
of them unknown to me personally. In many cases 
I have embodied the information which they have 
given me, and made no acknowledgment of it in 
the text, because my purpose has been to eliminate 
foot-notes and bibliography from a book which can 
make no claim to completeness. 

My friends Mr. C. B. Williams and Mr. V. H. W. 
Dowson have allowed me to draw upon them for 
several illustrations. Fig. 11 is from a photograph 
taken by Mr. F. W. Green, and to him and to the 
Director of the Geological Survey of Egypt I wish 
to express my gratitude. For Fig. 32 we are in- 
debted to Dr. R. I. Pocock and the Zoological Society 
of London ; for Fig. 34 to Mr. E. C. Stuart Baker 
and the Bombay Natural History Society ; for Figs. 
38 and 41 to Dr. J. Grinnell and the Museum of 



PREFACE vii 

Vertebrate Zoology, University of California, U.S.A. 
I am indebted to the Director of Agriculture, Iraq, 
for the data on which Fig. 8 is based : I am also 
extremely grateful to Miss A. M. Gayton and Mr. 
Engel Terzi for the line drawings. My friends 
Mr. C. B. Williams and Mr. W. E. Evans gave 
me invaluable assistance in the preparation of 
Chapter I (" The Desert Climate ") and Chapter III 
(" The Floral Environment "). To my wife, my 
sister, and my mother my best thanks are due for 
help in preparing the book for the press. 

P. A. BUXTON. 

Jerusalem. 

June, 1923. 



CONTENTS 

CHAP. PAGE 

Pbefacb V 

I The Desert Climate 1 

II The Soil and Watercourses .... 36 

III The Floral Environment 63 

IV Animals and the Physical Environment . 64 
^ V Animals and the Physical Environment (contd.) 81 

VI Relations between Animals and Plants . . 122 

VII Colours of Desert Animals . . . . 140 



iz 



LIST OF ILLUSTRATIONS 



FIG. 

1. Graph showing the Average Monthly Rainfall of five 

Places in the Great Palaearctic Desert . . p. 7 

2. Graph showing the Average Monthly Rainfall of five 

Places in the Indian Desert . . . . p. 8 

3. Graph showing the Average Monthly Rainfall of four 

Places in the Deserts of the Southern States of the 
U.S.A. The distribution of rainfall shown in this 
graph is not characteristic of stations in every part of 
these deserts . . . . . . . p. 9 

4. Graph showing the Average Monthly Mean Shade 

Temperatures of three Places in the Great Palsearctic 
Desert p. 16 

5. Graph showing the Monthly Mean Maximum and Mean 

Minimum Shade Temperatures of four Places in the 
Great Palaearctic Desert . . . . p. 18 

6. Graph showing the Monthly Mean Maximum and Mean 

Minimum Shade Temperatures of three Places sit- 
uated on the Sea Coast of the Great Palaearctic 
Desert p. 21 

7. Curve obtained from Recording Instrument showing 

daily Fluctuation in Relative Humidity at Gizeh, 
Egypt, 20th-22nd March, 1922. The figures on the 
side of the graph represent percentages of humidity 
(C. B. Williams) p. 24 

8. Graph showing the Relative Humidity at Mosul, N. 

Mesopotamia, at 8 a.m. and 4 p.m. during an average 
Week in June and an average Week in December p. 25 

9. Graph showing the Mean Relative Humidity at Two- 

hourly Intervals for the Months June, July, August, 
and September at Mohammerah, Persian Mesopo- 
tamia p. 26 



xii LIST OF ILLUSTRATIONS 

FIG. 

10. Artificial Depressions in Sand Dunes at El Wad, S. 

Algeria, planted with Date Palms which are drawing 
on Subsoil Water. The sharp margin of the oasis and 
the utterly barren nature of the dunes are apparent. 
{Photo : V. H. W. Dowson, July, 1922) facing p, 42 

11. Ridge of Cretaceous Limestone hollowed and carved by 

Wind-driven Sand, at Umm Shersher, S. of Kliarga 
Oasis, Libya. (Photo : F. W. Green, Greol. Survey 
of Egypt) facing p, 42 

12. Date Palm growing in a Pit at El Wad, S. Algeria. The 

contrast between the flourishing palm which has 
tapped the subsoil water and the utter absence of any 
undergrowth is striking. The palm-leaves inserted in 
the sand in the foreground are intended to check 
drifting sand. (Photo : V. H. W. Dowson, July, 
1922) facing p. 44 

13. Bare Expanse of Salt Mud at the North End of the Dead 

Sea, Palestine, with two or three tufts of salt-loving 
bushes : within the historical era this area was 
beneath the waters of the Dead Sea. (P. A. Bux- 
ton, photo) facing p. 44 

14. Salt Patch in Lower Mesopotamia. The white area is 

covered with crystals of salt ; the darker margin lies 
a few inches higher, and is therefore slightly less salt : 
the few small bushes are Suseda. (V. H. W. Dow- 
son, photo) ..... facing p. 46 

15. Salt-loving Vegetation (Atriplex halimus, etc.) on 

the Plain of Jericho, Palestine. (P. A. Buxton, 
photo) ...... facing p. 46 

16 & 17. Hills near the Mouth of R. Jordan, near Jericho, 
Palestine. These hills contain such a high propor- 
tion of salts that they are almost entirely bare of 
vegetation. (P. A. Buxton, photo) . facing p. 48 

18. Wadi Nar, S.E. Palestine. This is typical of a certain 
type of rock desert, in which the strata of bare rock 
alternate with softer material ; it is full of crevices 
and on it grow a large number of spring flowers, and 
it contains caves (pages 104-105). Typical birds are 
Rock Doves, Black and White Wheatears (Saxicola 
lugens)^ Rock Partridge (Alectoris), Ravens (Gorvus 
ruficeUis), and Tristram's Grackle (Amydrus tris- 



LIST OF ILLUSTRATIONS xiii 

FIG. 

trami) ; among mammals, the Coney or Hyrax 
{Procavia). (P. A. Buxton, photo) , facing p. 50 

19. Sandy Bed of a " Wadi " near Gaza, Palestine. For a 

few days at a time this bed will flow rapidly : 
though subsoil water is available at no great depth 
no bushes grow in the bed of the wadi because of 
the winter floods. (P. A. Buxton, photo) facing p. 50 

20. Wide Bed of a Flood Channel near Jericho, dry except 

for a few days or even hours in the year, but bearing 
a rich flora of perennials because of the presence of 
subsoil water. (P. A. Buxton, photo) . facing p. 52 

21. Bed of a Wadi at Biskra in the Algerian Sahara, 

showing Bushes of Oleander (Nerium) and Tamarisk 
(Tamarix). (V. H. W. Dowson, photo) facing p. 52 

22. Wilderness of Judaea, between Jerusalem and Jericho. 

These chalky hills are covered with annual vegetation 
in March and April and for the rest of the year are 
bare, except for very inconspicuous perennials 

facing p, 54 

23. Wadi Kelt, Wilderness of Judaea, Palestine. On the 

left of the picture are various trees and bushes, wild 
and cultivated, owing their existence to the perennial 
water of the wadi ; they are in no sense in the desert. 
On the right, a couple of yards from the sharp edge 
of the oasis, is the barren wilderness, at this season 
(July) showing nothing but withered annuals and 
a few small bushes of perennials. For a general 
view of this country, see Fig. 22. (P. A. Buxton, 
photo) ...... facing p. 54 

24 & 25. Photographs taken within a few hundred yards 
of one another in February (Fig. 24) and June (Fig. 
25). The spaniel dog gives an idea of the depth of 
the annuals in spring and of their closeness to each 
other : in summer the earth is bare and the perennial 
Zizyphus bush is the only conspicuous plant. (P. A. 
Buxton, photo) .... facing p, 58 

26. Stony Hill-side on the Mount of Temptation, near 

Jericho, Palestine, showing spring vegetation (Feb- 
ruary) and in particular the broad tufted leaves 
of the Mediterranean Squill (Urginea). (P. A. 
Buxton, photo) .... facing p. 60 

27. Cahtropis procera (Asclepiadaceae), in the Plain of 



xiv LIST OF ILLUSTRATIONS 

FIG. 

Jericho, Palestine. This bush belongs to the third 
group of desert plants, the perennials which exist 
above ground at all seasons ; the leaves are succulent 
and contain great quantities of a bitter, milky sap. 
Fragments of dead annuals may be seen. (P. A. 
Buxton, photOj October, 1922) . . facing p. 60 

28. Graph showing the Number of Species of certain 

Families of Orthoptera present month by month in 
Collections made at Amara, Lower Mesopotamia, 
by W. E. Evans and the Author . . p. 66 

29. Graph similar to Fig. 28, showing the Monthly Prev- 

alence of the Fossors (" Solitary Wasps "), Bees, 
and " four families " of Hymenoptera (i.e. Fossors, 
True Wasps, Bees, and Ruby Wasps) at Amara p. 67 

30. Graph similar to Fig. 28, showing the Monthly Prev- 

alence of Pyrale and of Noctuid Moths and of all 
Families of Moths except Pterophorina, Tortricina, 
and Tineina p. 68 

31. Hairy-footed Jerboa (Jaculus jaculus) from Egypt. 

Notice the long hind-legs with reduced number of 
toes, and the long tail with a terminal tuft of hair, 
and the biped attitude. (Drawn from life by Miss 
A. M. Gayton) p. 75 

32. Under-surface of Right Hind-foot of Allactaga indica 

(A), Scarturus tetradactylua (B), and Jacultts jaculus 

(C). (After R. I. Pocock) .... p. 76 

33. East African Gerbil (Taterona vicina) from East 

Africa. This animal is typical of a very large 
number of species, most of which are found in 
various parts of the Great Palsearctic Desert. 
(Drawn from life by Miss A. M. Gayton) . p. 77 

34. Imperial Sandgrouse (Pterocles arenarius). (After E. C. 

Stuart Baker) .... facing p. 84 

36. Addax Antelope (Addax masomaculatus), Male, from the 

Sudan. (Drawn from life by Miss A. M. Gayton) p. 90 

36. Arabian Oryx (Oryx leucoryx), an Inhabitant of Water- 

less Sandy Desert. (Drawn from life by Miss A. M. 
Gayton) p. 91 

37. Persian Gazelle (Oazella subgtUturosa), from Kirkuk, 

Perso-Mesopotamian frontier. The gazelles are 
very widely distributed and the numerous species 



LIST OF ILLUSTRATIONS xv 

PIG. 

are found in a great variety of different tjrpes of 
country. (Drawn from life by Miss A. M. Gayton) p. 91 

38. Holes of Dipodomys deserti in Sandy Ground, Mellen, 

Arizona. (Photo : Dr. J. Grinnell, Museum of Verte- 
brate Zoology, University of California) facing p. 102 

39. Fore-feet of the following Lizards : — 

A. PhrynocephaliLs mystaceus ( X 1 J) 

B. Acanthodactylus scutellatus ( X 2) 

C. Scaptira grammica ( X 2) 

D. Callisaurus ( Uma) scoparius. (After Cope, *' Amer. 
Nat.," 1894.) 

E. Teratoscincus scinctis ( X 2) 

F. Stenodactylus guttatiis ( X 3) 

G. Ceramodactylus dorice ( X 3) 

(E. Terzi) . p. 119 

40. Hind-feet of the following Lizards: — 

A. Phrynocephalus mystaceus (X IJ) 

B. Acanthodactylus scutellatus (X 2) 

C. Scaptira grammica ( X 2) 

D. Callisaurus (Uma) scoparius, (After Cope, 
"Amer. Nat.," 1894.) 

E. Teratoscincus scincus (X 2) 

F. Stenodactylus guttatus (X 3) 

G. Ceramodactylus dorice ( X 3) . . . p. 120 

41. Giant Cactus (Cereus giganteus), in which were found 

Nests of Gilded Flicker and Screech Owl : near 
Potholes, Colorado River, California. (Photo : Dr. 
J. Grinnell, Museum of Vertebrate Zoology, Univer- 
sity of California) . , . . facing p. 130 

42. Typical Black Diurnal Tenebrionid Beetles of the Great 

Palsearctic Desert. A and B, Adesmia ulcerosa; C 
and D, Pimdia angulata. (E. Terzi) . facing p. 150 

43. Typical Black Diurnal Flies, from Palestine, belonging 

to different Sub-families of the Bombyliidae: (A) 
Bombylius fuscus (Bombyliinse) ; (B) Hemipenthes 
(Anthracinse) (near H. velutina). (E. Terzi) facing p. 152 



ANIMAL LIFE IN DESERTS 

CHAPTER I 
THE DESERT CLIMATE 

i. General, ii. Water, iii. Heat. iv. Relative Humidity. 
V. Wind. vi. Evaporation, vii. Light, viii. Summary. 

i. General 
A prominent authority has stated that the desert 
occupies one-fifth of the surface of the globe, an 
area equal to that of Africa. It is probable that 
the word desert was used in rather a wide sense, 
and it is certain that no one has yet arrived at a 
definition of the word which would be acceptable 
either to the biologists or to the meteorologists. 
One is accustomed to think of the desert as an 
area of the earth rendered unfit for normal life by 
its climate, but, as I hope to show later, there is 
no climatic factor, or combination of climatic fac- 
tors, which invariably produces desert ; in fact, a 
few deserts exist by reason of their geological 
constitution, though their climate is not particu- 
larly unfavourable to plant and animal life. As the 
causes which result in desert are diverse, it follows 
that the term is not capable of strict definition : 
the definition which I now put forward is admittedly 

1 B 



2 ANIMAL LIFE IN DESERTS 

unsound, because it looks not to the forces which 
produce the desert, but to the result of their action; 
not to the weather and soil, but to the plants and 
animals which can grow in the desert in spite of 
its physical conditions. I use the word " desert " 
to include places in which the climate is hostile 
to animals and plants, in which normal agriculture 
is impossible, and in which nearly all the existent 
forms of animal and plant hfe are modified to endure 
life in their pecuHar environment. I use the word 
" semi-desert," without exact definition, to describe 
country of which the climate is less hostile, and 
the flora and fauna less specialized, than that of 
a desert ; semi-deserts support cultivation at cer- 
tain seasons, and provide grazing, though it is 
often bad grazing, at all seasons. Let us also bear 
in mind that deserts grade quite imperceptibly 
into semi-deserts, and these into savannas, steppes, 
and downs, and that a country may be extreme 
desert at one season and covered with lush vegetation 
at another. Furthermore, deserts are not neces- 
sarily permanent or very ancient ; the buried 
civilization of Eastern Persia and Turkestan and 
the petrified forest near Cairo are sufficient evidence 
of this. 

Most of the extensive deserts lie a little to the 
north of the northern tropic, or a little to the south 
of the southern tropic ; they do not lie close to the 
Equator. Most of them lie in the northern hemi- 
sphere and are bounded northwards by steppe, 
that is to say, arid country with a covering of 
grass and other perennials and an abundant flora 



THE DESERT CLIMATE 3 

after the winter rain, and southwards by savanna, 
that is to say, arid grass land with a few trees. 
The largest of all deserts is practically continuous 
from the Atlantic coast of North Africa to North- 
west India and the heart of China. It includes 
the whole of Northern Africa down to about lati- 
tude 20° N., but excluding those parts of Morocco, 
Algeria, and Tunisia which border the Mediterranean : 
it includes also Egypt and Sinai ; Arabia, the 
Syrian Desert, and Mesopotamia ; Persia, Afghani- 
stan, and Baluchistan ; Transcaspia, Turkestan, and 
the Gobi Desert, in Central China ; and parts of 
the Punjab, Sind, and Rajputana. The whole of 
this vast area is inhabited by the same types of 
animals and plants, and these for the most part 
are derived from Europe and Northern Asia, and 
to a much smaller extent from equatorial Africa 
or peninsular India. The great desert is, in fact, 
an integral part of the " Palsearctic Region," which 
is one of the primary divisions into which zoolo- 
gists and botanists have divided the globe : this 
region includes all Europe, and Northern and 
Western Asia, and Africa as far south as the southern 
part of the Sahara (about latitude 20° N.). I pro- 
pose, therefore, to use the term " Great Palsearctic 
Desert " when referring to this tract. 

The great desert of Australia is probably the 
second in the world in point of size ; it includes 
the heart of the continent and reaches nearly to 
the west and south-west coasts. 

The North American deserts consist of several 
small areas in the southern and south-western 



4 ANIMAL LIFE IN DESERTS 

States of the Union, and in Mexico. The impor- 
tance of these deserts to the botanist, and in a 
secondary manner to the zoologist, lies in the fact 
that they have been more thoroughly studied than 
any other desert region in the world. The labora- 
tory at Tucson, Arizona, supported by the Carnegie 
Institution of Washington, and directed by Dr. 
D. T. Macdougal, has contributed immensely to 
our knowledge of the climatic and physical features 
of the surrounding deserts, and of the influence 
of these features upon the vegetation. 

Other desert areas are found in South- West 
Africa and along the coast of South America, 
from latitude 5° to 30° S., in Eastern Patagonia 
and Western Argentina. Quite small areas of 
desert occur in many parts of the world, and any 
area of sand dune very closely resembles desert 
in the scarcity of available moisture, and in the 
specialization of its flora. 

It is not to be understood that any area described 
above as desert is uniformly so, either in its physical 
condition or in its flora and fauna. In the belt 
occupied by the Great Palaearctic Desert there are 
certain very fertile spots, for example, the delta 
of the Nile, the highlands of Yemen, and the date 
groves of Basra, and a similar diversity is found 
in other desert regions. 

We shall now review the chmatic influences 
which contribute largely to make life in a desert 
impossible to any plant or animal which is not 
specially adapted to it. In the mind of every one 
the desert stands first for dryness, secondly for 



THE DESERT CLIMATE 6 

heat ; and though this conception is not strictly- 
accurate, I propose to be guided by it. I shall 
therefore deal first with the supply of water and 
second with the heat and cold experienced in 
deserts. The available moisture and the current 
temperature together determine the amount of 
water-vapour present in the air, and I shall deal 
with this next. This will be followed by some facts 
relative to winds, because air movement is the result, 
in part at any rate, of the rapid fluctuations in the 
temperature to which these bare spaces are sub- 
ject. The discussion of wind leads us naturally 
to consider evaporation, which results from the 
presence of moisture and the combined action of 
heat and of air movements. The meteorological 
statistics which are quoted do not give very accurate 
information of the conditions to which the desert 
plants and animals are exposed. The instruments 
with which they are taken are generally exposed 
in a ventilated white-painted screen : the organisms 
which we are studying live on the surface of rocks, 
and in holes, and in a variety of other natural 
habitations. 

ii. Water 

It may be admitted at once that relative lack of 
moisture is a characteristic feature of all deserts, 
but it is not possible to state dogmatically that if 
the rainfall be below a certain figure the land will 
be desert, because the condition of the land depends 
not only upon rainfall but on many other climatic 
factors. It is generally accepted that a rainfall 



6 ANIMAL LIFE IN DESERTS 

of less than 5 inches (127 mm.) a year always pro- 
duces desert. On the other hand, there are areas 
between the Pacific Ocean and the Californian 
ranges of mountains, and in the Jordan Valley, 
which are desert though they receive 18 inches 
(460 mm.) of rain. In the first area the causes 
are the very high winds to which it is exposed, 
and the fact that most of the rain falls in winter, 
when it is of little service to the plants. In the 
second area, the lower end of the Jordan Valley 
and the land round the Dead Sea, the cause is the 
salinity of the soil. One concludes that it is un- 
profitable to devote much attention to the mean 
annual rainfall because the number of inches re- 
ceived is of less importance than certain peculiarities 
in its distribution through the seasons and through 
successive years, and because such factors as soil 
and exposure are also of prime importance. 

The rainfall in deserts is always very unevenly 
distributed throughout the months and the seasons, 
and unless one or more dry seasons of several 
months' duration occur, the condition of the land 
is not desert or even semi-desert. The graph 
(Fig. 1) shows the seasonal distribution of the 
rainfall which is characteristic of most places in 
the Great Palsearctic Desert. It will be seen that 
there is a dry or nearly dry season in summer, 
averaging six months, and a relatively wet season 
in winter. In the deserts of South Australia a 
similar alternation of dry hot weather and wetter 
cold weather occurs with regularity. 

The fact that the rainless period and the hot 



THE DESEET CLIMATE 7 

period coincide is of great importance to the vege- 
tation, which has to protect itself simultaneously 
against drought and heat : furthermore, the dry 
and hot period is very long. 

Within the limits of the Great Palsearctic Desert 
there are a few places which do not have a cold 



XII I II ill IV V VI VII VIII IX X XI XII 
3 in.T — ' ' — ' — ' ' ' ' — ' — ' — ■ — ' — r 75(u m. 




SOmm 



25 mm. 



Tashkent.TurKestan 



> Baghdad, Mesopotamia. 



o.oooChaman. Baluchistan Port Said, Egypt. 

Bahrein. Persia. 

Fig. 1. — Average Monthly Rainfall of Five Places in the Great 
Pal^iarctio Desert. 



wet season and a hot dry season. The area of the 
Indian desert (Fig. 2), in Rajputana, Sind, and the 
Punjab, is an exception, as owing to the monsoon 
the majority of its rain falls in July or August : 
in most stations in this area a small fall of rain 
occurs also in early spring. 



XII 



ii iir IV V VI VII VIII IX X XI XII 




XII III VI , IX Xlt 

Multan, Punjab Montgomery. Punjab. Jaisalmer.Rajputana. 

Karachi, Sind. » » . » o Dera Ismail Khan, N.W.F. Province. 



Fig. 2. 



-Average Monthly Rainfall op Five Places in the Indian 
Desert. 



THE DESERT CLIMATE 



9 



At many stations in the North American deserts 
the distribution of the rainfall resembles that which 
has just been described in the Indian desert (Fig. 3). 
The heaviest fall occurs in the summer, and a 
definite winter rain occurs in many places, so that 



XII I 11 III IV V VI VII VIII tX X XI XII 
ain.T"-' — ' — ■ — ■ — ' — ' — ■ — ' — ' — ■ — ■ — nbm. 




-50 mm. 



25 mm. 



oo ceo Tucson, Arizona 
- - S^George. Utah 



Fort Mohave, Arizona. 
Calexio, California. 



Fig. 3. 



-Average Monthly Rainfall of Four Places in the Deserts 
OF THE Southern States of the U.S.A. 



The distribution of rainfall shown in this graph is not characteristic of stations in every part 

of these deserts. 



there are two short dry seasons, in early summer 
and in autumn, in the North American and in the 
Indian deserts. At a large number of stations in 
the arid parts of North America only one rainy season 
is recorded, either in midsummer or in midwinter. 
So far, then, as moisture is concerned the conditions 



10 ANIMAL LIFE IN DESERTS 

in the deserts of India and in some of those of North 
America are much less rigorous than they are in 
most parts of the Great Palsearctic Desert : firstly, 
because the season of great heat is not also the 
season of great drought ; secondly, because the 
periods of drought are shorter as there are two dry 
and two wet seasons in the year ; and, thirdly, 
because in the majority of stations a little rain falls 
in nearly every month of an average year. If the 
rainfalls which are shown graphically in Figs. 1-3 
are studied it will be seen that either one or two 
dry periods per year is characteristic of all the 
places. In certain places these dry periods are 
much more extended, for the precipitation is quite 
irregular in its occurrence, and an intense desert 
results. Hayward found mimosas dead at Kidal in 
the South Sahara after five years without rain ; 
one must suppose that, as trees had been able to 
grow, the normal conditions were not utterly 
unfavourable to plant life, but an unusually long 
dry spell killed, no doubt, not only the mimosas but 
other plants as well, and with each plant species a 
host of insects, spiders, and other animals dependent 
on it. A year after Ha3rward made his journey 
across the Sahara Hartert was in Tidikelt, in the 
Central Western Sahara (1912). He found that 
rain had been very deficient for twenty years and 
as a result the Chenopodiaceous plant Traganum, 
which Rohlfs found growing in thickets in 1864, 
had died completely, even to the very roots. 

Mrs. Forbes has recorded that when she was at 
Kufara (Libya) in 1921 no rain had fallen for seven 



THE DESERT CLIMATE 11 

years, and it is probable that throughout a great 
part of the Libyan Desert and of the Western Sahara 
the rainfall is so slight and so irregular in its occur- 
rence that it makes little difference to the plant 
Hfe. Such plants as exist at all, and they are very- 
few, are dependent on subsoil water. 

Prolonged droughts have been recorded from 
many other deserts. As we have seen, the rainfall 
in the American deserts normally falls twice yearly, 
and is distributed through nearly every month : in 
spite of this it is on record that no measureable 
rain fell at Bagdad, California, from October 3, 1912, 
to November 8, 1914 ; a drought of over a year 
occurred at Indio, California, from November, 1893, 
to January, 1895. 

It may be stated as a general rule that the rainfall 
in desert places, even in places in which it is relatively 
regular, is liable to very great variation from the 
monthly and annual averages. This variation in- 
tensifies the struggle between the plants and animals 
and their environment, and is an important factor 
in the production of a desert. Angot suggested that 
the ratio between the maximum and the minimum 
annual rainfall of a spot could be used as an index 
of its agricultural possibilities. He believed that 
conditions were very unfavourable to agriculture in 
places in which the annual minimum rainfall was 
less than one-third or one-half of the annual maxi- 
mum. It is known, however, that an even greater 
disproportion than this can occur in places which 
are by no means desert, and we cannot say that a 
great irregularity in the amount of annual rainfall 



12 



ANIMAL LIFE IN DESERTS 



is found only in desert areas or that it is an invariable 
characteristic of the desert climate. It occurs very 
generally in the more pronounced deserts, and the 
following are striking examples : 





Annual Rainfall, inches. 




Place. 






Ratio 








(max. = 100). 




Min. 


Av. 


Max. 




Salton Sea, California 


trace 


2-74 


71 


0-1 : 100 


El Paso, Texas .... 


2-20 


9-23 


18-30 


120 : 100 


Yuma, Arizona .... 


0-60 


3-26 


11-41 


5-3 : 100 


Mohave, California . 


2-20 


4-97 


21-34 


10-3 : 100 


Tucson, Arizona .... 


5-26 


11-58 


24-17 


21-7 : 100 


Wargla, Algerian Sahara 


nil 


3-55 


8-27 


0-0 : 100 


Beni Ounif , Algerian Sahara 


0-50 


? 


8-50 


5-9 : 100 


Baghdad, Mesopotamia . . 


2-00 


7-29 


17-30 


11-6 : 100 


Basra, Mesopotamia . . 


210 


6-60 


10-70 


19-9 : 100 


Roeburn, Australia . . . 


013 


1 


42 


0-32 : 100 



It might be supposed that the number of rainy days 
per month or per year would be closely correlated 
to the monthly or annual precipitation, but this is 
not the case, for very great variation occurs in the 
amount of rain which falls on the average rainy 
day. In some desert climates it falls in minute 
amounts, and the number of rainy days may therefore 
be relatively large. This is characteristic of the 
South AustraHan Desert. At Oodnadatta, for in- 
stance, one-third or even one-half of the annual 
precipitation (4-68 inches : 118 mm.) is in amounts 
of less than 0-15 inch (4 mm.) : such minute 
amounts of water do not moisten the soil to an 
appreciable depth, and are very quickly evaporated. 



THE DESERT CLIMATE 



13 



unless one minute fall rapidly succeeds another. 
We need to distinguish between the actual rainfall 
and that part of it which reaches the roots and so 
becomes available to plants, and subsequently to 
animals. 

In other desert climates the opposite condition 
occurs, for the rain falls in large amounts on a very 
few days in the year. This is characteristic of very 
many deserts and may be so extreme that a single 
day's downpour exceeds the total rainfall of an 
unusually dry year. As examples one may quote 
the following figures : 



Place. 


Annual Average 


Day's abso- 
lute Maximum. 


Month. 


in. 


mm. 


in. 


mm. 


Bairam Ali 
Golodnaia Steppe 
Andijan .... 

Basra 

Amara, Mesopotamia 
Jodhpur, India . 


505 
1105 

9-60" 

6-60 

8-0 
13-63 


128 
278 
242 
167 
203 
347 


1-62 
3-97 
2-91 
3-10 
6-75 
10-00 


44 

101 

61 

78 

171 

253 


March 

November 

October 

November 

November 

August 



Such excessive rainfall is comparatively un- 
available to plants and animals because a great 
proportion of it runs off the surface of the ground 
into the river beds, and only a small part soaks into 
the soil at the place where it fell. The torrent 
which is produced in the stream bed is extremely 
destructive to plant and animal life (page 50). I 
conclude, then, that statistics of the average number 
of rainy days per month, or year, or of variation 



14 ANIMAL LIFE IN DESERTS 

from that average, give little information to the 
biologist. 

It is probable that dew is of extreme importance 
to the desert flora and fauna, but as practically no 
reliable statistics relating to actual dew-fall have 
been published, I am compelled to leave the matter 
in a very unsatisfactory state. It would be of great 
interest to biologists if i^eteorological observatories 
situated in deserts would accumulate information as 
to the amount of dew which actually falls under 
natural conditions, and the seasons and regularity 
of its fall. 

To sum up, the ordinary meteorological statistics 
are enough to assure us that the aridity of deserts 
is great ; they do not, however, tell us the whole 
truth, for three reasons. The first is that much of 
the recorded rainfall is not to be reckoned as " avail- 
able moisture," because a large proportion falls in 
heavy downpours which run off the surface of the 
ground into the water channels, and in some places 
an equally large proportion falls in such small 
amounts that it fails to penetrate the soil before it is 
evaporated. The second reason is that rain which 
faUs in the cold season, when vegetation is inactive, 
is of little value to the plants ; the third, that from ^ 
year to year the climate deviates widely from the 
normal. A certain flora may adapt itself to grow 
in a given spot, but may be exterminated by several 
unusually severe summers, after it has been estab- 
lished for several years. Shortage of water, and 
particularly shortage at seasons when the plant's 
requirements are large, is a most important factor 



THE DESERT CLIMATE 15 

in the production of deserts, but is by no means the 
only factor, and under certain circumstances places 
can be utter desert in spite of receiving a liberal and 
not ill-distributed supply of water. 



iii. Heat 

The temperature is of fundamental importance to 
the flora and fauna, not only for its own sake, but 
because it influences the humidity of the air and the 
evaporation of moisture. It is generally realized 
that the climate of a desert may be intensely hot ; 
it is equally true, though not so well known, that it 
may be extremely cold. Considerable daily and 
yearly range of temperature is a characteristic of 
the chmate of all great land areas, and we are 
justified in presuming that the extremes of tempera- 
tures of the desert are partly due to the fact that 
most desert areas lie in the centre of large land 
masses. This presumption is supported by the fact, 
to which we shall return later, that desert areas 
which lie close to the sea are not subjected to 
extremes of heat and cold. But we must not 
attribute the range of the temperature exclusively 
to the continental position of deserts, because the 
extremes encountered in deserts are much greater 
than they are in other continental areas ; and we 
beheve that the very great fluctuations of tempera- 
ture are due very largely to the bareness of the soil 
and the clearness of the sky. The radiant heat of 
the sun is not impeded either by cloud or by vegeta- 
tion from striking directly on the soil, which is 



16 



ANIMAL LIFE IN DESERTS 



warmed very rapidly to a high temperature. The 
hot surface of the earth then warms the lower layers 
of the atmosphere by conduction, and produces 
high air temperatures. At night, on the other hand, 
there is no blanket of vegetation to hinder loss of 
heat from the ground. Therefore much of the heat 
which has accumulated during the day in the 



Fig. 4. 



Xli I II 



IV V VI VII VIII IX X XI Xl> 




40^ 

^ Wadi Haifa. Egypt. Helwan, Egypt 

Babylon, Mesopotamia. 



-Average Monthly Mean Shade Temperatures op Three 
Places in the Great Pal^la.rctic Desert. 



superficial layers of the soil is radiated into space 
between sunset and sunrise. 

The monthly average temperatures of certain 
desert stations are shown graphically in Fig. 4. 
Two things are apparent : very high temperatures 
are attained in deserts, higher in fact than are ever 
reached in many places closer to the Equator, and 
very wide annual ranges of temperature are char- 



THE DESERT CLIMATE 



17 



acteristic. Almost any place in any desert will 
show these essential characteristics of the desert 
climate, provided it is not close to the sea. 

The contrast between a hot summer and a cold 
winter is shown not only by mean figures, such as 
those on which Fig. 5 is based, but even better by 
quoting the extremes of temperature which have 
been recorded at a given spot either in one year or 
in a series of years. The following are good 
examples : 



Place. 


Period 


Absolute Range. 


^'C. 


op 


Mosul, Mesopotamia .... 
Baghdad, Mesopotamia . 
Petroalexandrovsk, Turkestan . 
Tashkent, Turkestan . . . 
Ghardaia, Algeria .... 
Kasalinsk, Turkestan . . 


7 years 

28 „ 

10 „ 

10 „ 

1 year 

1 „ 


66-5 
57-8 
71-8 
70-2 

57 
88 


119 
104 
128 
126 
102 
158 



The following figures from Wadi Haifa (Anglo- 
Egyptian Sudan) are interesting because they show 
that though the normal range of temperature is 
great the occasional range is very much greater : 
the coldest month is January, with a mean lowest 
reading of 7-8° C. (46° F.); the absolute lowest 
reading in twenty-one years was — 2-2° C. (28° 
R); the mean highest reading is 41-1° C. (106° F.) 
(June), the absolute highest being 52-5° C. (130° F.) 
in April. It is clear that a slight frost, occur- 
ring once in a score of years, at a place in which 
the thermometer does not pass below 7-8° C. 

o 



XII I II 



IV V VI vn VIII IX X XI XII 




.♦- '-•♦♦' 



♦^ ,♦ 



■25 

^^ Jacobabad, SInd. — — Ghardaia, Algerian Sahara. 

Chaman. Baluchistan. ♦♦♦♦♦> Nukus, Turkestan. 



-20 



-30 



Fig. 5. — Monthly Mean Maximum and Mean Minimum Shade Tem- 

PERATUBES OF FoUR PLACES IN THE GrEAT PaL^EARCTIC DeSERT 



18 



THE DESERT CLIMATE 19 

(46° F.) in an average year, might devastate the 
flora. 

The daily range of temperature is scarcely less 
striking than the yearly, and is characteristic of all 
desert areas except those in close proximity to the 
sea. Cannon quotes figures which show that the 
extreme daily range of temperature recorded during 
three years at In Salah and Wargla in the Algerian 
Sahara is about 36-40° F. (20-22° C.) in the winter 
months and about 50-52° F. (28-29° C.) in the 
summer months. The average range of temperature 
on a single day in Baghdad, Mesopotamia, is 21° F. 
(11-7° C.) in January and December, and 31° F. 
(17-2° C.) in August and September. But though 
the daily fluctuation of temperature is generally 
highest during the hot months it appears that the 
greatest range which has ever been recorded in a 
single day was observed in December at Bir Milgha 
in Southern Tripoli by Rohlfs : he recorded a range 
of 68° F. (37-8° C), from 31° F. to 99° F. (- 0-5° C. 
to 37-2° C), within twenty-four hours. 

Many other instances of extremely rapid change 
of temperature are on record : Paulsen observed the 
shade temperature to be 37°, 68°, and 82° F. (3°, 20°, 
and 28° C), at 6 a.m., 9 a.m., and 1 p.m. in sand 
desert in Transcaspia. He also records the following 
figures at Tachta, on the Murgab River, on the 
23rd of June : 

6 a.m. Shade temperature 78° F. (25-5° C). Sun temperature 

93° F. (34-0° C.) 
8 a.m. Shade temperature 85° F. (29-5° C). 



20 ANIMAL LIFE IN DESERTS 

11 a.m. Shade temperature 104° F. (40-0° C). Sun tempera- 
ture 122° F. (50° C.) 
3 p.m. Shade temperature 109° F. (43-0° C). Sun tempera- 
ture 129° F. (54° C.) 

It wiU be noticed that enormous fluctuations in 
the temperature of the day, and of the year, are 
generally recorded from such places as Kasalinsk, 
Petroalexandrovsk, and Tashkent, in which the 
effect of desert conditions is reinforced by a position 
in the centre of a great land mass. On the other 
hand, certain places which are close to the sea are 
not liable to extremes of temperature, but are 
veritable deserts. Fig. 6 shows the monthly average 
maximum and minimum temperatures of El Arish, 
Aden, and Bahrein, all of which are in desert areas, 
on the coast of the sea. One concludes that great 
daily and annual range of temperature is a common 
element of desert climates, but not an essential 
characteristic. The bright sun shining unimpeded 
on the desert soil heats it very rapidly, so that 
by midday the temperature of its surface greatly 
exceeds that of the air above it. 

Our knowledge of the temperature reached by 
the surface of the soil is slight, but I hope shortly 
to publish records which show that in summer in 
South Palestine the surface of clay desert rises about 
36° F. (20° C.) beyond the shade temperature at 
midday. Nearer the Equator no doubt even higher 
readings would be secured, but in Palestine surface 
readings of 122-140° F. (50-60° C.) are normal. 
Prezhevalsky has recorded similar figures for the 
Gobi Desert, and adds that the surface of the soil 



THE DESERT CLIMATE 



21 



may be as cold as — 16° F. (—26-5° C.) in winter. 
The highest readings which have so far been taken 
of the surface of the soil were taken on bare sand ; 
e.g. readings of 183° F. (84° C.) on the Loango 
Coast, close to the Equator, and Augieras' record of 
172° F. (78° C.) on a sand dune in the Sahara. The\ 
surface soil reaches such a high temperature by day 



F XII I II III IV V VI VII VIII IX X XI XII 




El Arish, Sinai. Aden, Arabia. 

Bahrein, Persian Gulf. 

Fig. 6. — Monthly Mean Maximum and Mean Minimum Shade Tem- 
peratures OF Three Places situated on the Sea Coast of the 
Great Paljearctic Desert. 



that it does not cool completely during the ensuing 
night : as a result the minimum temperature 
reached by the surface of unshaded soil at night may 
be several degrees above the minimum temperature 
of the air (C. B. WilHams). It is only the superficial 
layer of the soil which is liable to these great fluctua- 
tions of temperature. 



22 ANIMAL LIFE IN DESERTS 

At Tucson, Arizona, in June, the temperature 
ranges daily through about 17° F. (10° C.) at a 
depth of 6 inches (15 cm.) in the soil, and over about 
2° F. (1° C.) at a depth of 10 inches (25 cm.) ; at 
the same season the shade temperature ranges over 
about 57° F. (37° C). Therefore at 6 inches (15 cm.) 
the daily fluctuation is about one-quarter of that 
of the air, and at 10 inches (25 cm.) it is only about 
one-thirtieth. Results which are essentially similar 
have recently been obtained by C. B. Williams in 
the desert near Cairo, Egypt, in July. The same 
investigator sends me the following data taken in 
April, 1922, at Luxor, Egypt, on cotton land which 
had been irrigated three weeks previously : air 
temperature 86° F. (30° C), soil surface 131° F. 
(55° C), soil at 3 inches (7-5 cm.), 81° F. (27° C.) ; 
at the same time the relative humidity of the air 
was about 15 per cent., and the relative humidity 
3 inches deep in the soil 98 per cent. These observa- 
tions may be taken as typical of others which have 
been made in South Algeria and other deserts. It 
will be seen that an animal would very easily reach 
equable conditions by burrowing, and that it would 
pass through a very great range of temperature and 
humidity as it entered or left its burrow during the 
middle of the day. 

iv. Relative Humidity 

The rainfall and the temperature of the desert 
have been discussed : upon their interaction depends 
the relative humidity of the air. It is defined as the 
amount of water- vapour which the air contains com- 



THE DESERT CLIMATE 23 

pared with the amount which it would contain if it were 
saturated with moisture from a flat surface of water 
at the same temperature. Relative humidity might, 
of course, be expressed as a vulgar fraction ; we could 
say that it was " one-third," meaning that the air 
contained a third of the amount of water-vapour 
which it could hold if saturated at the particular 
temperature under discussion. But it is generally 
more convenient to express the humidity in per- 
centages, the figure 100 representing saturation. 
The amount of water- vapour which the air can hold 
varies very greatly with the temperature, and it 
rises constantly as the temperature rises, so that a 
much greater amount of water-vapour is required 
to saturate a certain volume of air when it is warm 
than when it is cold. Suppose, for instance, that 
the air is saturated with water-vapour in the cold 
early morning, and that the actual amount of 
moisture in the air remains constant throughout the 
day : then the relative humidity will fall steadily as 
the temperature rises, because the air when warm 
could contain much more moisture than it actually 
does contain. 

This is what happens in most parts of the world 
on most days in the year. Among masses of dense 
vegetation and in damp places it is hardly noticeable 
because, however warm the air becomes at midday, 
it can still saturate itself from the wet soil and the 
vegetation. But in deserts the difference between 
midday with its low relative humidity, and the night 
with its high relative humidity, is extremely pro- 
nounced, because, as we shall see later, fl.uctuations 



24 



ANIMAL LIFE IN DESERTS 



of temperature are excessive, and there is little 
moisture available to increase the humidity of the 
air when its temperature rises. There is, therefore, 
a great contrast between the forest type of climate, 
with a very constant humidity, and the desert type, 
in which the humidity fluctuates widely in each 
period of twenty-four hours. 

In point of fact such a range of relative humidity 

Monday -^mt— -Tuesday >f<^- Wednesday-^ 

19 P.!4t r2 24 12 I 








Fig. 7. — Curve obtained from Recording Instrument showing Daily 
Fluctuation in Relative Humidity at Gizeh, Egypt, 20th-22nd 
March, 1922. 

The figures on the side of the graph represent percentages of humidity. (C. B. Williams.) 



as is shown in Fig. 7 does not occur from one year's 
end to another in many tropical forests, yet at 
Gizeh, Egypt, it is a normal daily occurrence during 
the summer. The curve of which Fig. 7 is a repro- 
duction was actually made during the end of March, 
1922, and shows that the humidity can drop from 
saturation to 20 per cent, in a few hours. Fig. 8, 
which shows the daily fluctuation (8 a.m. and 4 p.m.) 



THE DESERT CLIMATE 



26 



of relative humidity at Mosul, Northern Meso- 
potamia, during an average week in June and an 
average week in December, shows this point equally 
clearly. Very similar figures are obtained if the 

Sun. Mon. Tues: Wed. Thurs. Fri Sat. 

484848484848 




Fig. 8. — Relative Humidity at Mosul, N. Mesopotamia, at 8 a.m. and 

4 P.M. DURING AN AVERAGE WeEK IN JUNE AND AN AVERAGE WeEK 

IN December. 

mean of a series of readings is taken. Fig. 9 repre- 
sents the mean relative humidity taken at intervals 
of two hours every day from June to September, 
at Mohammerah, near Basra. The daily fluctuation 
in the humidity is, of course, less striking because 



26 



ANIMAL LIFE IN DESERTS 



this figure is based on average readings for that 
period, and the fluctuation would be even more 
remarkable were figures available, not from Moham- 
merah itself, which is on the Karun River among 
date palms, but from a spot two or three miles from 
it in bare desert country. 

Relative humidity varies very greatly within very 
short distances. Observations taken among a few 
palms, or in a cave or house, show a humidity 
very much less variable and generally higher than 



6?..n. 8ajii lOam. IZfwon Zptm. 4 p.m. 6p.m. 




Fig. 9. — ^Mean Relative Humidity at Two -hourly Intervals for the 
Months June, July, August, and September at Mohammerah, 
Persian Mesopotamia. 



that which is prevailing a few yards away in open 
desert. 

It is generally true that the greatest fluctuations 
in relative humidity occur during summer, and this 
depends largely on the fact that the temperature 
fluctuates more during a summer day than a winter 
day (page 19). Rapid and wide alterations in the 
relative humidity are therefore one of the many 
chmatic factors which combine to attack both plants 
and animals in summer, in deserts. 



THE DESERT CLIMATE 27 

The ordinary statistics of relative humidity pub- 
lished by official meteorologists are very unsatis- 
factory for the biologist. In many places readings 
are only taken in the morning and evening, and the 
full stress of extremely low humidity which oppresses 
the flora and fauna at midday passes unrecorded. 
Furthermore, readings are often taken at a place 
convenient to the observer, seldom out in the desert, 
and the readings of humidity suffer perhaps more 
than any others because of the variations which 
occur between places a few yards inside or outside 
an oasis. It is also to be remarked that readings 
are sometimes taken at 8 a.m. and 8 p.m., the two 
times at which the humidity is changing most rapidly. 
If, therefore, the reading is taken a few minutes 
too soon or too late a considerable error may be 
produced. 



V. Wind 

Rapid fluctuation in the temperature of the surface 
of the desert, and of the air above it, results in air- 
currents, which are generally greater in summer than 
in winter. At any rate, in the Great Palaearctic 
Desert a calm during the middle of the day is rare, 
and in many places winds of constant direction are 
experienced at this season. The sirocco is a hot 
easterly or southerly wind which blows in Palestine, 
Algeria, and other parts of the Mediterranean littoral ; 
the shamal, in Mesopotamia, blows from the north- 
west for many days at intervals all through the 
summer. During June, July, and August, which 



28 ANIMAL LIFE IN DESERTS 

are the windiest months of the year, 75 per cent, of 
the wind, and an even higher proportion of the 
stronger winds, are from this quarter. The sirocco 
and the shamal are two examples of the strong 
winds from a certain quarter, which blow with 
regularity in many deserts, but other and more 
violent regular winds are on record. 

At Menjil in North- West Persia a wind of great 
violence and regular occurrence blows whenever the 
sun is shining brightly on the Persian plateau. It 
is caused by the rising of the air which has been 
warmed by the hot plateau, and the consequent 
inrush of unwarmed air from the surrounding areas. 
At Menjil this is concentrated in the gorge of the 
Safid Rud, a river which here cuts its way through 
the Elburz Mountains, and a constant violent wind 
blows through the gorge all the day long, throughout 
the summer. This wind is of such strength that one 
can only walk against it with the greatest difficulty, 
and I have seen a loaded camel entirely unable to 
make headway against it ; tents can only be pitched 
during the hours of relative calm in early morning 
and late evening, and when securely pitched are 
generally ripped to shreds. Even more violent winds 
have been experienced in many desert areas, but 
few of them are of such regular occurrence as the 
Menjil wind. Augieras, for example, has recorded 
that in February, 1915, a violent wind kept him 
prisoner under the lee of a rock at Erg Chech in the 
Western Sahara for no less than nine days, and a 
month later he experienced a gale which carried a 
camel saddle 200 metres. The effect of wind-driven 



THE DESERT CLIMATE 29 

sand upon rock is illustrated in Fig. 11 (facing 
p. 42). 

The hot air which rises from contact with the 
heated desert sometimes makes its way upwards in 
vortices, or dust-devils. The dust-devil is a rotating 
column of air, and is generally seen on very hot days 
on which a moderate breeze is blowing. It is very 
sharply delimited, and owing to its load of debris, 
dust, and bushes, it is easily visible. It moves 
slowly about in the desert, following the direction 
of the wind rather irregularly. The height of the 
vortex is variable ; a century ago Lane measured 
one of 750 feet in Egypt and saw others taller, but 
the majority were shorter ; they were continuous 
columns reaching up from the ground for several 
hundreds of feet. Normand observed dust-devils 
at Samarrah in Northern Mesopotamia, some of 
which were at least 300 metres high, though only 
about 5 metres wide at the base. Sometimes these 
vortices lose contact with the ground, but maintain 
their existence at very great heights. Flying officers 
in Mesopotamia have encountered vortices of this 
sort whirling upwards at a height of 5,000 feet above 
the ground and still carrying dust and debris. Even 
a very small dust-devil is violent ; I have had my 
shirt stripped from my back by a vortex which 
seemed to be only a dozen feet in diameter, and 
during the operations in Mesopotamia and North- 
West Persia it was no uncommon sight to see a 
particular tent struck and emptied of its contents 
by a small vortex, which left untouched other tents 
only a few yards away. Larger vortices are much 



30 ANIMAL LIFE IN DESERTS 

more devastating ; in 1918 a very large camp at 
Balad Ruz, north-east of Baghdad, was struck by a 
dust-devil of unusual size, which carved its way 
through the camp, leaving a lane in which not a 
single tent was standing. Heavy articles of kit were 
blown as much as 200 yards through the air, and 
an officer of my acquaintance was scooped out of 
his tent with all his camp furniture, and dropped 
twice, the second time with several broken ribs. 

The effect of wind on other climatic conditions 
is various. A hot dry wind causes a rapid and 
considerable drop in the relative humidity, and 
generally a rise in temperature. Often, however, 
the wind causes a drop in temperature, because it 
mixes the lower layers of the atmosphere, which 
have been heated by contact with the hot earth, 
with the higher layers which have not been so heated. 
A wind heavily laden with sand or dust, and blowing 
for many hours on end, may cause a most marked 
drop in the day's temperature, by shielding the land 
from direct sunlight. 

vi. Evaporation 

Though on one hand the rainfall is meagre, on 
the other the evaporation is excessive in all deserts 
and at nearly all seasons. The rapidity with which 
water evaporates, whether from the superficial layers 
of the soil or from hollows in which it has accumu- 
lated, is caused by the high diurnal temperatures, 
by the direct rays of the sun beating down from a 
cloudless sky on bare earth unprotected by a covering 
of vegetation, and by the unimpeded action of the 



THE DESERT CLIMATE 



31 



wind. Figures are available from a limited number 
of desert stations giving the number of inches of 
water which would be evaporated from an open 
surface of water by the month or by the year. These 
figures do not represent what actually happens in 
the desert, because very soon after a fall of rain the 
surface of the soil is dried and evaporation practically 
ceases. But if they are taken in conjunction with 
the figures for annual mean rainfall they represent 
very vividly the discrepancy between the water 
upon which the plants can draw and the desiccating 
effect of the desert climate and sun. This ratio 
between possible evaporation (e) and actual rainfall 
(r) is of very great interest to biologists, and it is 
probably one of the most important factors in 
determining whether a place will or will not be 
desert. So far as we know it is high in all desert 
regions, and it is not high in regions which are not 
desert. 

The following examples show the very high pos- 
sible evaporation in deserts, and the ratio between 
this and the actual rainfall : 



Place. 



Yuma, Arizona . 
Piute Dam, Utah 
Tucson, Arizona . 
Mohave . 
Cahuilla, California 



Rainfall 

(Mean), 

Inches (r). 



3-26 
8-61 

11-58 
4-97 

17-35 



Evapora- 
tion, 
Inches (e) 



100 

61-2 

90 

95 
116 



e/r. 



30-7 
7-1 
7-8 

19-1 
6-7 



Cannon has given the following figures, which 
show that at Laghwat and Ghardaia the discrepancy 



32 



ANIMAL LIFE IN DESERTS 



between rainfall received and possible evaporation 
is immensely and irregularly increased in the summer 
and autumn months, the very period when the other 

Table showing the ratio between evaporation and rainfall month 
by month in 1908, at two stations in the Algerian coastal zone 
and two in the Algerian Sahara. Evaporation has been 
calculated as from a free water surface. Readings from a 
Piche evaporimeter have been corrected. 





Jan. 


Feb. 


Mar. 


Apr. 


May. 


June. 


July. 


Aug. 


Sep. 


Oct. 


Nov. 


Dec. 


Gran . . 


1-3 


1-9 


1-6 


1-3 


17-4 


8-5 


59 


146 


18 


2-45 


3-4 


4-4 


Algiers . 


0-6 


1-3 


0-5 


M 


22-3 


11-7 


219 


28-8 


5-0 


1-0 


1-2 


11 


Laghwat 


31 


4-7 


9-8 


203 


7 


373 


421 


21 


25-9 


14-2 


154 


104 


Ghardaia 


8-9 


233 


81-4 


629 


38-9 


699 


166 


25-6 


66-9 


23-2 


49-7 


225 



forces of nature aU combine to make life impossible 
for any plant or animal except those specialized for 
life in a desert. The ratio is lower and less fluctuat- 
ing in the coastal non-desert stations (Algiers and 
Oran). Cannon states that if the annual evaporation- 
rainfall ratio of the littoral zone be taken as unity, 
that of the high plateau is 3-7 and that of the desert 
(average of Laghwat, Ghardaia, and El Wad) is 18-6. 
It will also be appreciated that in an unusually 
dry year the evaporation-rainfaU ratio will be vastly 
increased, so that, at a time when the mere drought 
is pressing hardly on the flora and fauna, an increased 
discrepancy between rainfaU and evaporation is also 
thrown into the scale against them. If, for instance, 
the normal evaporation-rainfall ratio for Mohave, 
with a mean rainfall of 4-97 inches (125 mm.) is 
19-1, then in the dry year with a rainfall of only 
2-20 inches (55 mm.) the ratio would be 43-2, if we 



THE DESERT CLIMATE 33 

suppose that the evaporation in that particular year 
was average. Judge, then, how great must be the 
fluctuations in this important ratio in spots in the 
Libyan Desert where the rain falls only once in 
every four or five years, and where the evaporation 
is believed to be 150 inches or over. 

vii. Light 

The uninterrupted sunHght of Egypt, even in 
the winter months, is a thing which has arrested 
the attention of every tourist. Accurate records 
of the intensity of sunlight in deserts are scarce, 
but one can at any rate recall a few general truths. 
The sun's rays consist not only of light rays and 
heat rays, but also of ultra-violet and other rays 
which are known to exercise very definite influences 
on living matter. All these rays, but particularly 
the ultra-violet rays, pass more readily through 
dry than through damp air ; their effect on plants 
and animals is therefore much more potent in summer 
than in winter, for in summer the days are longest, 
the sun most nearly vertical at midday, clouds are 
absent, and the amount of water- vapour in the air 
at its lowest. 

Viii. SUMMAEY 

We have discussed individual elements of the 
climate ; let us now try to consider the cHmate 
as a whole, built up of these and other component 
elements. If we were to study only the average 
meteorological statistics for a number of places in 
the Great Palsearctic Desert we should reahze at 



34 ANIMAL LIFE IN DESERTS 

once the great contrast between the summer and 
the winter. The summer is rainless ; it is very- 
hot by day but much cooler at night, and the rela- 
tive humidity of the air varies very greatly in the 
twenty-four hours ; the daily fluctuation in the 
temperature of the air is exceeded by that of the 
temperature of the surface of the soil ; the sky 
is clear, the day long, the atmosphere dry, and the 
sun vertical or nearly so at midday, and it foUows 
that the effects of the sun's heat and chemical 
rays are very great ; the winds are strong and 
constant in direction, and occasionally violent and 
destructive ; evaporation is extremely active and 
far exceeds the amount of moisture received by 
the soil. In every respect the climate in winter is 
different from that in summer. It is information 
of this sort which we shaU glean from mean 
statistics, but they only teU us a part, and an 
unimportant part, of the truth. It is not the 
contrast between the seasons, immense though it 
is, which is the essential character of the desert 
climate. 

Rather it is the extraordinary deviations from 
the mean which mark out the desert chmate as a 
thing quite distinct. It is to the maximum and 
minimum figures, not to the means, which we must 
look if we are fully to reaHze the difficulties with 
which desert plants and desert animals have to 
contend. It is not the regular succession of summer 
and winter, however dissimilar, but the occurrence 
of long droughts, torrential rains, unusual frosts, 
violent whirlwinds, and other irregular phenomena 



THE DESERT CLIMATE 35 

that have prevented the covering of the ground 
with vegetation and the peophng of the vegetation 
with a normal fauna. It is also to be constantly 
remembered that many different factors go to deter- 
mine that land shall be desert : here it is drought, 
there it is wind ; in other places, as we shall see 
in the next chapter, it may be shifting sand, or 
saHnity of the soil, or absence of drainage or of 
humus. 



CHAPTER II 
THE SOIL AND WATERCOURSES 

The physical environment of a creature includes 
not only the climate of its habitat, but also certain 
factors which may collectively be termed " geo- 
logical." Among them are the type of soil on which 
it lives, the flatness or hilliness of the country, and 
its exposure to or protection from sun, wind, and 
rain, and the existence of supplies of water other 
than rain and dew. 

The influence of the geological environment upon 
the desert plants and animals is almost as important 
as the influence of cUmate, though less attention 
has been given to it. The prevalent notion that 
deserts are uniform stretches of sand dune is entirely 
erroneous, for desert soils exhibit a wide range of 
chemical and of physical characters. The soil of 
a desert is commonly gravel, or sand, or bare rock, 
or sunbaked mud ; other types of soil are found, 
and almost the only soils which never occur are 
those which result from the presence of plentiful 
vegetation, for instance loam and peat. The scarcity 
of humus is probably an important factor tending 
to prohibit all but a few specialized plants from 
colonizing deserts; in fact this, and the general 

36 



THE SOIL AND WATERCOURSES 37 

badness of the drainage, are common characteristics 
of desert soil. 

It is to be remembered that various types of desert 
pass gradually into one another. Clay desert passes 
by insensible steps through clay desert containing 
a few stones to stony desert ; at the other end of 
the scale stony desert may contain so many large 
stones and so little fine soil that it is not far removed 
from rock desert. Further, an area which is uniform 
so far as soil is concerned may be bare desert in 
one ' place, semi-desert or steppe in another, by 
reason of the presence of windbreaks, or of different 
exposure, or of other factors. One cannot draw 
sharp lines of delimitation between the different 
types of desert, nor between areas which are desert 
and others which are semi-desert. The Hmits of a 
desert are indefinite not only in point of space ; they 
vary also with time. This is so characteristic a 
feature, and so striking when one has actually seen 
it, that I shall return to it again and merely state 
in passing that bare earth tenanted by a few special- 
ized plants and animals and exposed to the full rigour 
of a desert summer may enjoy a delightful spring 
during which it is carpeted with lush, unspecialized 
flowering plants and teeming with bees and butter- 
flies. For two or three months one may truly say 
that the desert has vanished (Figs. 24, 25, facing 
p. 58). 

It is impossible to understand the relationships 
between the soil of a desert and its flora and fauna 
without understanding the powers which are 
possessed by all soils, in varying degrees, of holding 



38 ANIMAL LIFE IN DESERTS 

water, of allowing it to sink through them, and of 
raising it from lower levels by capillarity. In 
general we may say that evaporation of water 
from the sm^face of the desert soil is due to the heat 
of the sun, the movement and dryness of the air, 
and the nakedness of the earth. Evaporation 
(page 30) exceeds rainfall in deserts, except in 
very short periods in the year : therefore the sur- 
face of the soil is normally quite dry. But at 
short distances beneath the surface one frequently 
finds a proportion of moisture which is surprising, 
and the proportion rapidly increases at sHghtly 
greater depths : it is impossible in a general dis- 
cussion to quote figures, and the depth varies with 
such factors as type of soil, interval since last rain- 
fall, and the depth of the permanent moisture in 
the soil. The explanation of the dryness of the 
surface and dampness of the deeper soU is that 
after the soil has been saturated by a fall of rain 
the surface rapidly dries : this drying process 
penetrates to greater and greater depths, becoming 
slower and slower, because the action of wind 
is cut off, and the diffusion of the damped air is 
retarded by the superficial layer of soil which is 
already air-dry. There is continual upward mov^ 
ment of moisture from the depths of the soil in 
which water was accumulated when the rain fell, 
and to which in certain cases water is brought 
by seepage from springs, rivers, or water-bearing 
strata. This upward movement depends on capil- 
lary attraction, which enables the water to rise 
above the level at which it would naturally lie, by 



THE SOIL AND WATERCOURSES 39 

penetrating the minute spaces between the soil 
particles. There is then an upward movement of 
water, from the subsoil, due to the capillarity, and 
a downward movement of the level from which 
evaporation is taking place in the soil. This down- 
ward movement is slower the farther from the sur- 
face it is taking place : at a certain point the 
upward and downward movements balance one 
another, and at this level the moisture in the desert 
soil remains constant, unless equilibrium is upset 
by fresh rainfall or increased evaporative power of 
the air, or some other disturbing factor. These 
facts have a practical appUcation. Cultivation of 
arid land is sometimes rendered possible by the 
employment of a machine which reduces the sur- 
face of the ground to fine powder (" dust-mulch "). 
This layer of fine powder, penetrated by corre- 
spondingly minute air-spaces, decreases the upward 
diffusion of the air which has saturated itself with 
moisture in the soil. The decreased upward diffu- 
sion results in decreased evaporation, and equili- 
brium is disturbed, to be re-established nearer the 
surface, at a point where the upward movement 
of the moisture once again balances the lessened 
evaporation. But as the moisture in the soil now 
lies at a higher level it is possible to plant and raise 
crops which could not have come to maturity 
without the aid of the " dust-mulch " (Livingstone). 
Bearing it in mind, then, that terms such as 
" sand desert," " gravel desert," are not capable 
of exact definition, or of exact geographical de- 
limitation, let us turn our attention to some of the 



40 ANIMAL LIFE IN DESERTS 

commoner different types of soil of which the desert 
may consist, and the various problems which have 
to be faced by organisms which inhabit the sand, 
or gravel, or rock, or mud. 

The sand is in many ways the most hostile of 
all environments. Its surface is very smooth, and 
offers little impediment to the wind. As has 
been said already, winds in any desert tend to be 
strong, sometimes violent : in sandy desert their 
action is unchecked by any obstacle. These winds 
are detrimental to the plants ; they break leaves 
and branches, they greatly increase evaporation 
from the soil and transpiration from the plant, 
and they carry abrasive particles of sand and soiL 

As the surface of most sandy areas is frequently 
in motion, even in the absence of sand-storms, it 
is extremely difficult for plants to colonize them. 
Young seedlings are overwhelmed, tender shoots 
are damaged by blown sand, and roots are laid bare 
to the sun. In certain places where the surface of 
dunes is particularly unstable no vegetation of any 
sort grows. In the Indian deserts, according to 
Blatter and Halberg, the fairly copious monsoon 
rains may temporarily consoUdate the surface of a 
dune which at other seasons is unstable. SeedUngs 
of various plants then spring up and, as the sand 
dries, some individuals of certain species hold their 
own, while the rest die. In all parts of the world 
spots which are less wind-swept are colonized by 
special plants, many of them grasses, which re- 
semble the marram of our own coasts in their habit, 
and after they have established themselves and to 



THE SOIL AND WATERCOURSES 41 

some extent consolidated the dune, a number of 
other plants are able to take root. These all tend 
to hold together the sand around their roots and 
to protect the surface of the dune from the wind 
and from evaporation. There is therefore a ten- 
dency for the dune to become more and more 
solidified and immobile, and more and more covered 
by vegetation : each plant that grows and then 
dies increases by a little the organic constituents 
of the dune, and by that much decreases one of the 
factors which render colonization of its surface so 
difficult. 

The relationships of sand to rain falling on it are 
remarkable. Water which falls on its surface sinks 
in with extreme rapidity, and to a considerable depth: 
and the tendency for the water to rise by capillarity 
is slight, because the sand-particles are relatively 
large. Therefore the rain which falls on sand is 
of no use to short-rooted plants. On the other 
hand, as it sinks rapidly and as the surface of the 
water remains at a considerable depth, loss by 
evaporation is less than in any other type of desert. 
In fact, the sand dune is a sponge, and most of 
the water which it receives it holds. The con- 
ditions favour long-rooted perennials rather than 
other types of plant. The sparse fl.ora of a sand 
dune in the Great Palsearctic Desert often consists 
solely of perennial grasses and deeply rooted switch 
bushes, but in parts of Transcaspia, where sand 
overlies impervious loess at no great depth, quite 
luxuriant vegetation grows even in summer 
(Paulsen). 



42 ANIMAL LIFE IN DESERTS 

In places where sand overlies an impervious 
rock, copious water is available for the cultivation 
of deep-rooted plants, which flourish when once 
they are established. Just to the south of Jaffa, 
in Palestine, is a large area of shifting dunes, with 
a sparse flora and fauna, closely adapted to their 
environment. The land was in fact indubitable 
desert until certain astute people discovered that 
vines would grow luxuriantly in depressions among 
the dunes. In these places water can be obtained 
at all seasons by sinking wells to about 6-8 feet, 
and when once the young vines are established 
they grow well and produce grapes in the dry, hot 
autumn, at a time when the dunes appear a little 
more dry and barren than usual. 

Another plant which grows well in deep sand is 
the date palm. Its root system attains a remark- 
able length while the plant is still yoimg and smaU, 
and reaches deep-lying supplies of water. Hartert 
and other travellers have described the conditions 
of date culture at El Wed in the Algerian Sahara 
(Figs. 10 and 12). The town and gardens are in 
imminent danger of being overwhelmed by moving 
dunes, and are constantly afflicted by violent sand- 
storms. Subsoil water is plentiful at a considerable 
depth in the sand, and the inhabitants excavate 
large pits in the sand, and at the bottom plant 
offsets of palms. At first watering by hand is 
necessary, but after a few months the young palm's 
roots reach the subsoil water : the owner's task then 
is to remove the sand which threatens to cover 
his trees, and at this task he labours almost un- 




Fig. 10. — ^Datb Palms (Jiiuwing in Artificial Depressions in Sand Dunes 
AT El Wad, S. Algeria. {Photo : V. H. W. Dowson. July, 1922.) 




'£ 



Fig. 11. — Ridge of Cretaceous Limestone carved by Wind-driven Sand, 
AT Umm Shersher, S. of Kharga Oasis, Libya. {Photo : F. W. Green, 
Geol. Survey, of Egypt.) 



THE SOIL AND WATERCOURSES 43 

ceasingly with his basket ; he also dusts his vege- 
tables with a small brush to free them from drifted 
sand. Figs. 10 and 12 show clearly the contrast 
between the flourishing palm which has tapped the 
subsoil water, and the barren dunes which surround 
it. The palm-leaves inserted in the sand in Fig. 12 
are intended to check wind-driven sand: there is 
no undergrowth because the water supply is so 
deep. 

The Nefud, or areas of sand dune in Arabia, are 
relatively fertile and support so much indigenous 
vegetation that they are recognized winter and 
spring pastures. Camels grazing in the Nefud in 
spring are able to dispense with drinking for long 
periods. Doughty records that the inhabitants 
planted a dune at Boreida with tamarisks, and that 
after one year the trees were established and no 
longer in need of artificial watering. 

Sand deserts of various types may be distin- 
guished : bare, shifting dunes, more stable dunes 
covered with plants, and undulating plains. In 
the desert west of the Nile, and in many other 
places, areas of loose sand alternate with outcrops 
of rock, and the rock is often etched and carved 
with fantastic shapes by the wind-driven sand 
grains (Fig. 11). Sand desert of one kind or 
another is said by Cana to occupy 700,000 square 
miles of the Sahara, an area equal to about one- 
fifth of the whole ; according to Augieras, dunes 
up to 200 metres in height exist in the Western 
Sahara : no other area of equal extent is known. 
The Takla Makan, in Eastern Turkestan, is a sandy 



44 ANIMAL LIFE IN DESERTS 

desert of considerable size ; Sven Hedin states that 
he travelled for several days in it without seeing 
any sign of vegetable life. 

Deserts of clay, fine river silt or loess, present 
contrasts to sand deserts in nearly every particular. 
The soil is extremely fine in texture. The surface 
is generally flat (Figs. 13 and 14) or nearly so, 
smooth, and hard ; rain which falls upon it tends 
to run off rapidly either into watercourses or into 
depressions from which it rapidly evaporates. Fur- 
ther, these finely grained soils have a high capacity 
for holding water ; therefore that portion of the 
rain which sinks into them does not penetrate to 
a great depth, but is held in the superficial layers 
of the soil and rapidly lost by evaporation. For 
these two reasons soils of this type waste a large 
proportion of the rainfall which they receive. For 
a similar reason they are wasteful of any ground 
water with which they may be endowed : as the 
particles of the soil are very fine and the interstices 
between them minute, the force of capiUary attrac- 
tion exerted by them is great : ground water is 
therefore carried up towards the surface and made 
available for shallow-rooted plants ; but large 
quantities of it are evaporated. 

The ground water brings up with it mineral 
salts, which are left in the supei-ficial layers of the 
soil as it evaporates. The rain water, which runs 
into a shallow depression and then evaporates, tends 
to concentrate these salts in patches. As most of 
these deserts are flat they are devoid of good sur- 
face drainage, and as their soil is so fine in texture 



s\ 




— x 



W -19^ ■ " ■ . ; ••; :i f V ..V V u V-l i t'T . 





THE SOIL AND WATERCOURSES 45 

and so consolidated, there is no subsoil drainage. 
One finds therefore that some degree of saltness 
is characteristic of flat clay or mud deserts. In 
the parts which lie a little higher than the rest, 
and from which the salt is washed by the rain, 
the salinity is slight, and plants, many of them 
specially adapted to growth in salt places, may be 
found. In the depressions it is common to find 
an incrustation of crystals of salts, and an absence 
of vegetation of any kind whatsoever (Fig. 14), 
or one may find that the ground is slimy, even in 
dry weather, owing to the hygroscopic properties of 
the salts which it contains. Around the margins 
of these salt patches one finds an intermediate 
zone inhabited by salt-loving plants, such as grow 
at home on sea marshes. In Fig. 14 the plants 
on the right are Suaeda : they are growing on land 
which is a few inches higher than that on the left, 
which is covered with white salt-crystals. Fig. 15 
shows Atriplex halimus and other bushes which 
love salt, growing on a plain of salt mud. 

The salts found in these positions vary. Common 
salt (sodium chloride) is, I believe, always present, 
but in less proportionate amounts than in sea water. 
In Transcaspia magnesium and sodium sulphate 
are common, and calcium sulphate (gypsum) occurs. 
In Mesopotamia different proportions of chlorides 
and sulphates of sodium, calcium,, and magnesium 
all occur in relatively large quantities, in the salt 
and alkaline lands. 

Figs. 16 and 17 show a peculiar type of salt 
clay desert which is found at the lower end of the 



46 ANIMAL LIFE IN DESERTS 

Jordan VaUey, and in certain spots round the 
margin of the Dead Sea. The soil here is so im- 
pregnated with salts that in spite of an annual 
rainfall of 16-18 inches, and in spite of the excellent 
surface drainage provided by these slopes, no 
vegetation exists. My friend, Mr. Raczkowski, of 
the Department of Agriculture, Palestine, made 
an analysis for me of the surface soil of one of the 
hillocks shown in the plate ; the analysis was made 
in February, just after the winter rains which one 
might suppose would have washed much of the salt 
out of the superficial layer of soil. Nevertheless, 
the analysis revealed the presence of 0*58 per cent 
of sodium sulphate, 0*57 per cent of sodium chloride, 
and 36-13 per cent of sodium carbonate. Any 
one of these salts in such high proportions would 
be sufficient to prevent the growth of plants, except 
forms specially adapted to exist on salt soils : their 
united effect is to render these clay hills abso- 
lutely devoid of plant life at all seasons of the 
year. 

The loess of Transcaspia and Turkestan and the 
fine silt of the plains of Lower Mesopotamia are 
very fertile if they are irrigated and if provision 
is made for the removal of the water after it has 
flowed upon the land, so that mineral salts do not 
accumulate unduly. In Southern Mesopotamia the 
rainfall is not inadequate, and combined with the 
annual flooding from the Tigris and Euphrates 
would be sufficient to sustain considerable vegeta- 
tion, were it not for the physical peculiarities of 
fine silt. Here, in fact, we have country which 





Fig. 14. — Salt Patch in Lower Mesopotamia. {Photo : V. H. W. Dowson.) 




Fig. 15. — Salt-loving Vegetation on the Plain of Jericho, Palestine. 
{Photo : P. A. Buxton.) 



THE SOIL AND WATERCOURSES 47 

is desert, not because of its climate, but because 
of the physical characters of its soil. 

The fact that smooth, hard deserts of silt or 
clay or loess support a very small fauna is partly 
due to the small number of plants occurring, but 
also to the fact that natural shelter from sun, 
drought, wind, and light is difficult to obtain. 
Even species which are capable of excavating 
burrows for themselves are liable to be drowned 
out by every storm of rain. 

Very large areas of the Great Palsearctic Desert 
are composed of mixed stone and earth. This 
type of desert consists of varying proportions of 
stones, large and small, lying on and in clay or loess 
or fine earth of other kinds (Fig. 26). This mixed soil 
carries a relatively rich flora, if cHmatic conditions 
are not imfavourable. The finer element in the 
soil supports the flowers which it would naturally 
support if it occurred alone, and the presence of 
stones which hinder evaporation and by that means 
tend to conserve soil moisture, enables other plants 
to exist. In fact the mixed type of soil results in 
a rather varied flora, and this in turn increases 
the fauna. Apart altogether from their depen- 
dence on the plants, animals are more numerous 
in stony deserts because they find shelter from the 
cHmate under the stones. This point will be dis- 
cussed later (pages 100-101 ). Stony desert, and semi- 
desert, is very widely distributed in the Palsearctic 
region, for instance in the Northern Sahara, the 
south of Sinai and Palestine, and large areas in 
Persia, Afghanistan, and Baluchistan. 



48 ANIMAL LIFE IN DESERTS 

Gravel desert, a type which consists apparently 
of pebbles with very little fine soil to fill up the 
interstices, has been described by Blatter and Hal- 
berg in Rajputana, and by Thomas on the edge of 
the Libyan Desert, north-west of Cairo. The inter- 
vals between the individual pebbles allow the 
immediate escape of any rain which falls ; on the 
other hand, the surface of gravel desert is not 
liable to be moved by the wind. Gravel desert, 
as might be expected, supports a very poor flora : 
Thomas says that " standing in most places it is 
impossible to see a single plant anywhere around 
one. ... At a period when the annuals have 
disappeared I have traversed several miles on 
patrols, without seeing a single plant." Though 
he studied his area during and after the spring 
rains he was only able to identify eight flowering 
plants in the gravel desert. 

Outcrops of bare rock may occur in deserts of 
almost any type. Small areas of rock present 
intense difficulties to colonization by plants or 
animals : in any cHmate the plants growing on 
rock surface are rare, because soil is only found in 
small pockets (Fig. 18), and because nearly all the 
rain received runs off the rock at once : in deserts 
the difficulties are intensified. Larger areas of 
rock are less hostile to flora and fauna because they 
nearly always include patches of soil and little 
islands of plants. In most large areas of rock, 
caves occur, with their speciaUzed fauna and rela- 
tively stable climate. A reference to the animals 
which are found in desert caves will be found on 





Eigs. 16 and 17. — Hills of Salt Mud near the Mouth of R. Jordan, near 
Jericho, Palestine. {Photo : P. A. Buxton.) 



THE SOIL AND WATERCOURSES 49 

page 104. In Fig. 18 I have illustrated a type 
of rock desert in which strata of hard and soft 
calcareous rock alternate. On the softer large 
numbers of spring flowers grow : these valleys are 
full of caves, both natural and artificial. Typical 
birds in this type of country in Southern Palestine 
are Rock Doves, Wheatears {Saxicola lugens and 
others). Rock Partridge (Alectoris =Caccabis), 
Ravens (Corvus ruficollis), and Tristram's Grackle 
{Amydrus tristrami) : among mammals, Porcupines 
and the Coney or Hyrax (Procavia). 

The influence of watercourses upon desert life 
is very much greater than might be supposed. 
Many of them are temporary, fed by snow, or by 
rain faUing on some distant mountain mass, and run 
out into the desert plains, where they gradually 
disappear owing to evaporation and seepage into 
the soil. The length of such a river varies immensely 
with the season : at the end of a period of drought 
the whole bed may be dry (Figs. 19, 20, and 21) ; 
after a period of heavy rain a torrent may be pro- 
duced sufficient to flow several hundred miles down 
a bed which has been dry for years. One of the 
longest of these dry watercourses is the Wadi 
Rummah, which rises near Medina in the highlands 
of Western Arabia, and at one time crossed the 
peninsula to discharge its waters into the Shatt al 
Arab near Basra. It is more than a thousand miles 
long, though its course is now blocked by large 
areas of sand dunes and water never runs from 
end to end of it. In some of these torrent-beds 
bushes and other vegetation grow (Figs. 20 and 21) : 



50 ANIMAL LIFE IN DESERTS 

in others the floods are so violent, or the soil is so 
unfriendly, that nothing grows (Fig. 19). 

These apparently dry beds form Hnes along which 
subterranean water drains, and in many of them 
it may be found by sinking a weU to a depth of a 
few feet. This subsoil water determines the pre- 
sence of a relatively dense vegetation (Fig. 21), 
consisting often of a fairly large number of species ; 
these in turn provide food and shelter to very many 
animals. The bed of the stream gives Hfe lavishly ; 
as lavishly as it destroys it. A sudden heavy rain- 
storm, such as is common in deserts (page 13), 
falls, the water runs rapidly off the bare ground 
and produces a devastating flood. Shakespear saw 
such a flood as this in the Batin (lower part of 
Wadi Rummah) in Central Arabia ; twenty minutes 
of heavy rain converted the dry bed into a rushing 
torrent 3 feet deep, 50 feet across. Such floods are 
not rare in Arabia. Philby has suggested that the 
desolation of the once populous Wadi Hanifa was 
due to a great flood which obUterated the settle- 
ments in the bed of the Wadi, and spared those 
on the sloping ground around ; he records a flood 
in Wadi Dawasir which filled weUs, and destroyed 
a hamlet, and another which drowned 150 men, 
450 camels, and thousands of sheep, if local report 
is reliable. Palmer records a flood which destroyed 
forty bedawin and their flocks in the Wadi Solaf 
in Sinai, and doubtless examples might be multipUed. 
Certain desert areas are traversed by great 
perennial rivers, such as the Tigris and Euphrates, 
the Nile, and the rivers of Transcaspia. In Lower 



THE SOIL AND WATERCOURSES 51 

Mesopotamia and the Nile Valley, and on the great 
plain through which pass the Amu Dana (Oxus) 
and Syr Daria (Jaxartes), plant and animal life 
depend less on local rainfall than on the annual 
flooding of the ground at the time when the river 
is at its highest. The height to which the river 
rises varies greatly from year to year, and depends 
on precipitation and the melting of snow in far- 
distant regions. The Nile is under partial control 
and the height of its annual rise is more constant 
than it would otherwise be : the Tigris is not under 
control, and the Euphrates only to a very sHght 
extent. It follows that in a year of exceptionally 
high water great areas of Mesopotamia which would 
otherwise be unflooded are inundated in March and 
April and remain covered with water for several 
months. This not only keeps the soil of the plain 
moister than it would otherwise be in early summer, 
but materially modifies the summer heats, and 
appears to double or treble the number of insects 
which are on the wing throughout the whole sum- 
mer. On the other hand, this annual flooding of 
a flat land is very unfavourable to the burrowing 
animals and appears to limit the species of lizards 
and small mammals very materially. 

It is noteworthy that the majority of closed 
drainage basins, from which there is no outlet to 
the sea, are desert. This is probably due in the 
main to the fact that in them salts accumulate, 
until the increasing salinity of the area causes it 
to become desert. Examples are the great basins 
of Central China, Eastern Turkestan, and the Sahara, 



52 ANIMAL LIFE IN DESERTS 

into all of which rivers run from the surrounding 
uplands without ever making a sheet of water in 
the centre. Other closed basins, without outlet to 
the ocean but with inland seas or lakes into which 
they drain, are those of the Dead Sea and Jordan 
Valley ; the Caspian with the Mugan Steppe and 
the steppes of 'the Volga and Transcaspia ; the 
Sea of Aral with the Oxus and Jaxartes Rivers 
and the great plain of Russian Turkestan ; the 
Shotts (Chotts) of Southern Algeria and Southern 
Tunisia ; the Great Salt Lake in the State of Utah ; 
Death Valley and the Salton Sea in California ; 
and the Lake Eyre basin in Central Australia. All 
of these areas are desert, and the Dead Sea, the 
Caspian, the Sea of Aral, Death Valley, Salton 
Lake, and Lake Eyre are all beneath mean sea-level. 




Fig. 20. A Flood Chaxnkl near Jericho, dry except for a few 

DAYS OR EVEN HOURS IN THE YEAR. {PhotO : P. A. Buxton.) 




Fig. 21. — Bed of a Wadi at Biskra in the Algerian Sahara, 
SHOWING Bushes of Oleander {Nerium) and Tamarisk {Tamarix). 
{Photo : V. H. W. Dowson.) 



CHAPTER III 
THE FLORAL ENVIRONMENT 

I shall discuss the vegetation of deserts, not as a 
botanical problem, but because the plants are a 
very important element in the environment of the 
fauna. It will be appreciated that many of the 
characteristics of desert plants which are of great 
interest to the botanist, and to the study of which 
notable contributions have been made, appear to 
matter but Uttle to the zoologist, who is interested 
not in the plants themselves, but in the plants 
considered as a part of the surroundings of the desert 
animals. It would be rash to say that such things 
as the pitted stomata and highly concentrated sap 
of plants growing in dry places do not affect the 
fauna, but at any rate it is not at present apparent 
that they do so. I have therefore omitted these 
and a number of other points to which the botanists 
have devoted attention. 

It is impossible to draw up such a description of 
desert scenery and vegetation as would be appHcable 
to the deserts of aU the continents and both the 
hemispheres. It is, however, true to say that the 
prevaiHng tint for the greater part of the year is 
that of the soil, for the plants grow so far from one 

53 



54 ANIMAL LIFE IN DESERTS 

another that they do not colour the landscape, except 
for a short period after rain has fallen. In most 
deserts bushes are rare and tend to become con- 
spicuous features of the scenery, if they are present : 
trees are so rare that they are regarded with venera- 
tion by desert-dwelling races in more than one part 
of the world. At certain spots in the desert water 
is available in relatively large quantities : such spots 
are oases, and are characterized by a dense growth 
of vegetation, often consisting of plants which do 
not and cannot grow in the surrounding desert, and 
which are not found outside the oasis, until a second 
oasis is reached. This growth of vegetation provides 
food for a number of animals, many of which are 
specially dependent on one of the oasis plants, or 
for some other reason unable to live in the surround- 
ing desert. The edge of an oasis is usually extremely 
sharply defined : the plants of the oasis grow up 
to the edge of the area which has the abundant water 
supply, and there they stop abruptly. Fig. 23 
illustrates this admirably.^ On the left is a dense 
growth of poplar, fig, apricot, bramble, and many 
other wild and cultivated plants, dependent on a 
perennial spring in the bottom of a " wadi " : on the 
right, a yard or two away, is the " wilderness of 
Judaea," with no living plants except Atriplex 
halimus, and not many of that. The photograph 
was taken in July, after the spring annuals had died : 
their dried remains may still be seen. Fig. 22 gives 
a general view of the same country. 

Very few natural oases exist, and many of them 
1 See also Fig, 10, opposite p. 42. 




Fig. 22. — Wilderness or Jud^a, between Jerusalem and Jericho. 
{Photo : V. H. W. Dowson.) 




Fig. 23. — Wadi Kelt, Wilderness of Jud^a, Palestine. On the 

LEFT ARE VARIOUS TreES AND BuSHES ; ON THE RIGHT IS THE BARREN 

wilderness. {Photo : P. A. Buxton.) 



THE FLORAL ENVIRONMENT 55 

are only small thickets near such rivers as the Tigris 
and Zarafshan, which flow through deserts. Nearly 
all the larger natural oases have long ago been 
totally ruined by man, who has destroyed the 
characteristic and very local flora and fauna, planted 
carrots and cabbages and dates (Figs. 10, 12), and 
introduced along with them the common garden 
weeds and the common garden insect pests, so that 
to a naturaUst a " well-developed " oasis is one of 
the most uninteresting sights in the world. The 
water which turns a given part of the desert into an 
oasis may come from any source, from springs, or 
seepage from a water-bearing stratum, from a passing 
river, or even from an artificial canal or artesian well. 
The deserts of the Old World are great plains, 
and the vegetation is siu*prisingly monotonous and 
uniform over immense areas. Many genera and 
species of plants range from the western Hmits of 
the Sahara, or even from the barren parts of the 
Azores, Canary and Cape Verde Islands, eastwards 
to Sind and Turkestan. Conspicuous examples are 
the Colocynth {CitruUus colocynthus), the Saltbushes 
(Suceda and Salsola), and members of the genus 
Zizyphus (Fig. 25) ; very many others might be 
mentioned which are distributed over the greater 
part of the vast area. The uniformity of surface 
and of vegetation, which is so characteristic of the 
Old World deserts, is much less observable in 
America. MacDougal states that he found only 
thirteen species of flowering plants during a month's 
trip in the Libyan Desert : twelve of the thirteen 
belonged to very widely distributed species, and he 



56 ANIMAL LIFE IN DESERTS 

contrasts this with the fact that " many dozens of 
species are known from places in American deserts 
no larger than an ordinary farm, in single canons, 
or on one slope of unique environic combinations." 
He suggests that the reason for this lies in the 
comparative newness of the American deserts, which 
consist of relatively small plains and steep mountains. 
The environment is varied and the plants vary with 
it. In the course of ages these deserts will undergo 
a process of base-levelling, and will perhaps come to 
resemble the immense desert plains of the Sahara, 
Mesopotamia, and Transcaspia. By that time the 
conditions will be so uniform, and have altered so 
profoundly from those now prevailing in America, 
that very many species wiU have ceased to exist. 
The relatively unspecialized types, which have not 
adapted themselves too closely to their environment, 
will have spread widely and come to occupy vast 
areas. 

The plants which are found in deserts belong to 
special genera and species which are so modified in 
structxu*e, and in their manner of performing their 
vital functions, that they can support life under very 
unfavourable conditions. These modifications are 
so great and so fundamental that the transfer of a 
desert plant to a less severe environment, or of a 
seaboard plant to the Arizona Desert, was always 
followed by the death of the plant, in certain of 
MacDougal's experiments ; on the other hand, the 
transfer of plants to environments which were 
strange to them, but were not desert, resulted in 
quite a number of survivals. 



THE FLORAL ENVIRONMENT 57 

We have already seen that the rigours of a desert 
climate abate in many places for a short season 
every year. Plant life in deserts has suited itself 
to the cHmatic conditions in many ways, of which 
three are the most important. During the short 
period which follows the rain annuals are common. 
At the same season a group of perennial plants 
which persist through the dry months dormant 
underground produces its leaves and flowers. The 
third principal group of desert plants consists of 
perennials the structure of whose aerial parts is so 
profoundly modified that they can continue their 
vital functions throughout the year. We shall now 
examine each of these groups more closely. The 
first group, the annuals, is extremely conspicuous 
after rain, so much so that for the moment the 
desert is no desert, and the perennials, at other 
seasons so conspicuous, cease to attract our notice. 
The seeds of the annuals have survived a dry period 
of months or years and have resisted terrific heat 
and desiccation, but the stems, leaves, and flowers 
are not anatomically modified for life in dry places. 
The annual plants appear shortly after a fall of rain, 
carpet the ground to a greater or lesser extent, 
blossom in an incredibly short time, and then wither 
rapidly when the soil and the air become dry. 
Figs. 24 and 25, taken in the plain of Jericho in 
February and June, show this. The spaniel dog 
illustrates the depth and thickness of the spring 
annuals. This ephemeral vegetation depends directly 
upon the rainfall, and on it in turn depend a large 
number of forms of animal life. In some parts of 



58 ANIMAL LIFE IN DESERTS 

the deserts of America there are two rainfalls : that 
which occurs in December and January is followed 
by crops of flowers of winter annuals: as soon as 
the cold weather is passed : these then dry up and 
perish. The summer rains come and soak the ground, 
but the seeds of the winter annuals do not germinate ; 
instead, there comes up a crop of summer annuals 
which ripen seed soon after midsummer ; this seed 
lies dormant all through the cold weather, even 
though it is saturated by the winter rains. Whether 
the desert has one rainy season or two these annual 
plants add very greatly to the number of species 
and of individual plants occurring in an area ; in 
fact, a richness of flora is produced which for the 
moment far exceeds the inroads made upon it by 
the larger herbivorous animals : their number is 
Umited by their abiUty to exist through the long 
dry seasons. The smaller forms of animal Hfe, for 
instance, the insects, increase in numbers enormously 
as the annual vegetation grows, and Uke it rest in 
various ways for the rest of the year. 

The second large biological group contains plants 
which exist beneath the ground during the dry 
months in a dormant condition, and which produce 
leaves, stems, and flowers after rain has fallen. The 
perennial part of the plant is a bulb, corm, tuber, or 
fleshy root. It is essentially an organ for storing 
food, and it is by drawing upon these reserves that 
the plant is able to respond rapidly to rainfall and 
send up its flowers and leaves : there is no occasion 
for the storage of water, for these plants are active 
only at a season when water is abundant. Plants 



THE FLORAL ENVIRONMENT 59 

of this group are particularly common in the semi- 
deserts and deserts of Palestine, Sinai, Persia, and 
indeed in most parts of the Great Palsearctic Desert. 
Many of them belong to the Lily, Amaryllis, and 
Iris famiUes, and famihar examples are colchicum, 
squills (the broad leaves of which are shown on the 
right in Fig. 26), tuHps, asphodels, onions, and stars 
of Bethlehem. Their reserves of food are stored in 
different parts of the plant : in Stars of Bethlehem 
(Ornithogallum), onion (Alhum), and others, in 
closely packed leaf -bases constituting a bulb ; in 
iris, crocus, etc., in swollen subterranean stems 
(corms) ; and in the roots in asphodels and others. 

The third important group in the flora contains 
those perennial forms which are so specialized that 
they can exist above ground and perform their vital 
functions at all seasons. To this end they are 
modified in many remarkable ways ; roughly speak- 
ing, the modifications fall within two groups, those 
which tend to reduce the loss of water from the 
surface of the plant, and those which tend to preserve 
a store of water in the body of the plant. Many 
forms exhibit both types of modification. In the 
first group of adjustments to environment we find 
that the leaves are small or absent, or only produced 
after rain when the soil and the air are relatively 
damp ; at such times loss of water from the surface 
of the leaf is of less importance than during the dry 
season. In those plants in which the leaves are 
greatly reduced or absent the twigs and stems are 
green ; it is the chlorophyl in these organs which 
carries on the function of starch manufacture, a 



60 ANIMAL LIFE IN DESERTS 

function performed in ordinary plants by chlorophyl 
in the leaves. When leaves are present they are 
often extremely tough and leathery ; the cuticle, in 
particular, is greatly thickened and the surface is 
protected in many species either with wax or with 
resins, or with incrusted salts, or with densely 
matted hairs : it is beHeved that all these modifica- 
tions, which occur in desert plants of the most 
widely different famiUes, enable the plant still 
further to reduce the amount of water which it 
loses by transpiration. In all deserts a certain 
proportion of the plants become succulent, that is 
to say, develop the capacity of storing a considerable 
quantity of water. Succulence is not only a char- 
acteristic of desert plants, but of those growing in 
any environment in which the available moisture 
is limited: some succulents, for instance, grow on 
salt-marshes, others on rock surfaces and roofs and 
walls, even in damp cHmates. Most of the desert 
succulents are found in areas with a rainfall which is 
sHght but fairly regular, and they are not generally 
found in intense deserts and in cUmates without any 
regular precipitation. They are developed in an 
apparently capricious manner in certain deserts and 
not in others. For instance, the cacti, nearly all 
of which are succulent, some of them extremely so, 
are numerous both as species and as individuals in 
the deserts of the southern United States and of 
Mexico. In the arid parts of South Africa their 
place is taken by plants of the Spurge family 
(Euphorbiaceae), and some of these plants so closely 
resemble the cacti of the New World that they can 



THE FLORAL ENVIRONMENT 61 

barely be distinguished from them until they flower. 
This is an example of convergence, the production of 
very similar structures by plants which are not at 
all related to one another, as a response to similar 
environmental influences. On the other hand, succu- 
lents are rare in the Great Palaearctic Desert, speaking 
generally, and the cause is unknown, for in many 
places the conditions of weather and soil are such 
as appear to favour succulents in American and other 
deserts. The only noteworthy exception is the salt 
parts of the Great Palsearctic Desert : in these such 
genera occur as are familiar in saltings in many 
parts of the world. 

Nearly every part of the plant body, but most 
commonly stems and leaves, may be used for the 
storage of water. In the Cactus family, for instance, 
the stem is greatly thickened and often nearly 
globular : it is used for the storage of water, and 
MacDougal states that tree cactuses may contain as 
much as a thousand gallons. Succulence of the stem 
occurs also in spurges and many other families : in 
Southern Mexico there is an Ipomsea, a plant closely 
alHed to the convolvulus, which has a soft thick 
trunk containing water, and Beaucarnea, a relative 
of the Yuccas, is so charged with water that its 
trunk is 7 or 8 feet in diameter, though the tree 
itself is not above 25 feet high. An example of 
a plant with succulent leaves, Calotropis procera 
(Asclepiadacese) is shown in Fig. 27. 

It will be seen that there is a most interesting 
contrast between the second and third groups of 
desert plants. Members of the second group have 



62 ANIMAL LIFE IN DESERTS 

little need for a reserve of water, for they are only- 
active after rain when the soil is damp ; they store 
food in the form of starch and allied substances, 
so that when the rain is received they can at once pro- 
duce active growth. Members of the third group are 
active at all seasons ; they therefore are able to 
manufacture their own food as they need it : many 
of them possess storage organs, but they store water 
not food. 

The sap of many succulent plants is saUne or 
bitter : this appears to protect the plant from 
animals in many instances, but it does not follow 
that the primary function of the bitterness is 
protective. In certain instances it is known that 
the water accumulated by succulent plants is of use 
to animals ; for instance, the donkey can be watered 
with the juice of the giant cactus (Cereus giganteus), 
which is too bitter for man's use, and the barrel 
cactus (Echinocactus) furnishes several pints of fluid 
which even man drinks readily. 

Thorniness is possibly more characteristic of the 
third group of desert plants than succulence : it is 
a character common to the plants of deserts in all 
countries, and of every type of desert, and it is 
exhibited by herbs and bushes belonging to a very 
great number of different natural orders. It is 
found on the most varied parts of the plant body ; 
the stem may be thorny, and the leaves may be 
covered with thorns, or may themselves be trans- 
formed into thorns ; the fruits also may be thorny. 
It is believed by many that the thorns protect the 
plant against herbivorous animals. This point will 



THE FLORAL ENVIRONMENT 63 

be considered in greater detail in the chapter which 
considers the relationships between plants and 
animals in the desert. Here I shall only say that 
the view that thorns are defensive is difficult to 
maintain, except in a few special instances. On the 
contrary, it appears probable that the thorniness of 
the plants that grow in deserts is due rather to 
physical than biological influences. It is known 
that if a plant is grown in a dry atmosphere it 
produces a relative increase of various hard sub- 
stances at the expense of its starches and plastic 
materials ; it is also known that cultivation in a 
damp atmosphere retards the development of thorns 
in seedlings. It is therefore possible that the 
thorniness of desert plants is a purely physical or 
chemical phenomenon, and that any protection that 
the plant derives from it is purely incidental. 



CHAPTER IV 

ANIMALS AND THE PHYSICAL ENVIRON- 
MENT : GENERAL RELATIONSHIPS 

General Relationships 

We have considered the surroundings in which 
the desert animals live, and seen that the chmate 
and other physical factors are generally unfavourable 
to ordinary animal life. We shall now study some 
of the adaptations which enable the animals to 
overcome the obstacles of their physicietl environment, 
and to draw sustenance from the specialized flora of 
the desert. 

Every element of the desert climate is liable to 
rapid fluctuations, which are often quite irregular : 
and in many desert places the great heat and 
drought, and violent winds and other climatic factors, 
all combine during the summer to be most hostile 
to the flora and faima. 

The habit of aestivation in plants has been already 
referred to (pages 57-59). A similar habit is common 
in the invertebrate animals of desert faunas. In 
the present state of knowledge we can only attribute 
it in broad terms to the extreme hostility of the 
summer climate ; but it may well be that as we 
study the effects of varying temperature, or humidity, 

64 



ANIMALS— PHYSICAL ENVIRONMENT 65 

or other conditions, upon particular species, our 
knowledge will become more accurate. We shall 
perhaps find that in the case of one creature the 
cessation of activity during summer is induced by a 
mean temperature above a certain degree, or in 
another by a minimum daily humidity below a 
certain percentage. Until the particular effect of 
altered cUmatic conditions upon selected species of 
animals has been studied we cannot do more than 
record the facts, which are that the great majority 
of the invertebrata in deserts undergo periods of 
dormancy either in winter or in summer, or both. 

In Mesopotamia it is easy to notice that insects 
are commonest after the winter rains, during the 
temperate spring and early summer. From April 
to June nearly aU insect life is fully active, and its 
activity coincides with and follows the rapid growth 
and blossoming of the spring vegetation. During 
the hot dry months of summer the insects are not 
in evidence ; as the weather becomes cooler there 
is a distinct, though less evident, increase in the 
number of insects on the wing. Figs. 28 to 30 are 
compiled from collections made at Amara, R. Tigris, 
by Capt. W. E. Evans, R.A.M.C., and myseK. 
, It would scarcely be extravagant to claim that our 
collections are a fair random sample of the fauna 
of Amara at all seasons. We had few distractions 
and were deeply interested in entomology ; we each 
resided in Amara for almost exactly one year ; we 
felt that we were in an imknown land and there- 
fore collected everything, even species which were 
common, in long series when we could; we could 



66 



ANIMAL LIFE IN DESERTS 



identify none of our captures and therefore did not 
discriminate ; and we generally worked independ- 
ently, in different parts of the area round Amara. 
Fig. 28 shows the monthly occurrence and relative 
frequency of certain famiUes of Orthoptera. It wiU 
be seen that the Praying Mantis family was repre- 
sented by most species in April and September; 



ill fV 



VJ VII VIII IX 



XI XII 




Short-horned Grasshoppers. — Crickets. 

Mantis family Long-horned Grasshoppers. 



Fig. 28 — Number of Species of Certain Families of Orthoptera 

PRESENT month BY MONTH IN COLLECTIONS MADE AT AmAJIA, LoWER 

Mesopotamia, by W. E. Evans and the Author. The Months 

ARE SHOWN by RoMAN FiQURES, THE NUMBER, OF SpECIES] OCCUR- 
RING BY Arabic Figures. 

the Long-horned Grasshopper family in May and 
October ; and that of the Short-horned Grasshoppers 
in June and October. The Crickets, which are 
nocturnal and shelter by day under logs and in 
holes and cracks in the groimd, do not show this 
seasonal incidence ; the conditions to which they 
are exposed are different and they react differently 
to them. The Hymenoptera (Fig. 29) show similar 



ANIMALS— PHYSICAL ENVIRONMENT 67 

curves ; the Fossors are most abundant in June and 
September; the bees in July and September. 
The Ruby Wasps (Chrysids) and Wasps (Vespids) 
were represented by so few species that curves 
have not been constructed from them, but the 
curve for all four families shows maxima in June 
and September. Even the moths comply in the 
main with this rule, which could hardly be expected, 
as the majority of them are nocturnal, and shelter 



XII I II ill IV V VI VII VIII IX X XI XH 




Four families. Fossors 



Bees. 



Fig. 29. — Graph similar to Fig. 28, showing the Monthly Prevalence 
OF THE Fossors (" Solitary Wasps "), Bees, and " Four Families " 
OF Hymenoptera (i.e. Fossors, True Wasps, Bees, and Ruby 

Wasps) at Amara. 

by day in places in which they must be protected 
from the great heat and low humidity. The curves 
in Fig. 30 all reach maxima in May or June, and in 
September. 

Certain groups of insects showed a different 
seasonal prevalence, amongst others some of the 
butterflies, of which very few species were found at 
Amara. The Clouded Yellow {Colias croceus = 
edusa), Common White {Pieris rapce), and three Blues 
(Zizera karsandra, Tarucus halcanica, and T. mediter- 



68 



ANIMAL LIFE IN DESERTS 



ranece) were all on the wing from March to June and 
again from September to November. A few indi- 
viduals of several of these species were taken in the 
intervening hot months, but these species were rare 
at that season and clearly fall into the same group 
as the Orthoptera, Moths, and Hymenoptera (Figs. 
28 to 30). Three species, however, had totally 
different seasons. One " Blue " (Chilades gatba) 



XII I II III IV V VI VII VIII IX X XI XII 




■All families. Pyrales Noctuge. 



Fig. 30. — Graph similar to Fig. 28, showing the Monthly Prevalence 
OP Pyrale and of Noctuid Moths and of all Families of Moths 
EXCEPT Pterophorina, Tortricina, and Tincina. 



was abundant from June to August and was not 
taken at other seasons, though its food plant was 
always abundant and was in leaf all the summer and 
autumn ; the " Skipper " Parnara matthias was 
only taken from June to November ; and the 
common salmon-coloured Teracolus fausta from July 
to December. 

The apparent absence of this species in spring and 
early summer may be due to one of two causes. 
The Caper bush (Capparis spinosa), its food plant, 



ANIMALS— PHYSICAL ENVIRONMENT 69 

is bare of leaves till the warm weather is well 
advanced, and it is possible that the species Hes 
dormant through the spring as egg, or resting larva, 
or pupa, until the Caper bush is in fuU leaf. On 
the other hand, it is possible that even the mild 
winter of Mesopotamia is fatal to T. fausta in all 
stages, and that it recolonizes this country every 
spring by immigration from lands with warmer 
winters ; in Palestine it seems extremely probable 
that this species dies out every winter, and recolonizes 
the land every spring. 

It is convenient to mention here another Pierine 
butterfly which eats Caper, the species known as 
Belenois mesentina, although it was apparently 
absent from Amara. It is a species which often 
occurs in great numbers in very hot places, even in 
the hottest weather : for instance, along the North- 
West Frontier of India it is common from May to 
October, a season during which the other butterflies 
are scarce or not on the wing at all. It has an 
extremely wide distribution, from tropical Africa to 
India, and is by no means confined to deserts. This 
wide distribution is possibly due to its ability to 
continue active life at a time of year when heat 
and dryness have caused most butterflies to cease 
from flying, and this activity in the height of summer 
may in turn be due to the fact that the Caper is 
one of the not very numerous plants in full leaf at 
that season. 

It must be admitted that this study of the number 
of species of insects on the wing in various months 
is liable to one very grave criticism. Each group 



70 ANIMAL LIFE IN DESERTS 

of insects, in fact each species, finds this or that 
month favourable to it for a different reason. The 
mantises may be influenced by an abundance of 
other insects on which they prey. The bees or 
wasps may, for all we know to the contrary, time 
their emergence more by the flowering season of 
certain plants than directly by any cUmatological 
event. The moths may fly at midsummer, not 
because midsummer conditions suit them particu- 
larly, but because several months before there was 
abundance of herbage for their larvae. In fact, 
Figs. 28 to 30 represent facts which are the result 
of the action of very many factors : they cannot be 
used as a basis of a theory. If we wish to interpret 
the abundance of insects in a certain month, we 
must take individual species of insects and study 
their reactions to altered temperature, humidity, 
food, soil, moisture, etc. We are not justified in 
taking such curves as Figs. 28 to 30 and comparing 
them without further analysis with the meteoro- 
logical statistics, or the season of greatest plant 
growth. 

In the British Isles we are accustomed to think 
that the warmer the temperature to which insects 
are exposed, the more quickly do they go through 
the various stages of their Hfe-history. This is 
clearly a fallacy, because in Mesopotamia in many 
different families of insects active life is in abeyance 
during the hottest months. We can at present only 
guess at the cause ; it is probable that heat and 
humidity interact in such a way that neither factor 
can be considered separately : a certain high 



ANIMALS— PHYSICAL ENVIRONMENT 71 

temperature is optimum for the development of a 
certain insect only when the humidity is about a cer- 
tain figure ; if the humidity is much below that figure 
the temperature may be unfavourable or even fatal. 

The curves in Figs. 28 to 30 show clearly that the 
cessation of active Hfe in summer is less than that 
in winter. One is accustomed to associate the 
summer of Mesopotamia with fierce heat, acute 
discomfort and the sudden death of Europeans who 
were unable to avoid active work in the middle of 
the day : apparently to the adult insect the summer 
is less unfavourable than the winter, for it will be 
seen that January provides far fewer winged insects 
than July or August. Our conclusion, then, is 
this : that aestivation and hibernation are common 
phenomena among desert insects ; until we have 
accumulated a mass of detailed analysis we must 
accept it that these phenomena are, in a general 
way, due to the climate in summer and winter being 
unfavourable. 

Ants, as Wheeler has shown, adapt themselves to 
the desert seasons in several ways. In more ordinary 
surroundings some ants are insect-eaters, but very 
many Uve upon plant juices which they obtain either 
directly or from Plant-lice (Aphidse) and Scale 
insects (Coccidse) : in deserts they have to contend 
against periods of drought. Some of them therefore 
become extremely active predators, ranging far and 
wide and running with great rapidity. Many others 
collect seeds and pieces of dried plants, and depend 
upon this harvest for food and moisture during the 
summer. Others, again, collect plant juices, and 



72 ANIMAL LIFE IN DESERTS 

the secretions of Plant-lice during the season of 
active growth which follows rain, and store these 
fluids in the stomachs of certain specialized " worker " 
ants ; these become enormously distended with 
fluids, and are known as honey-pot ants, and from 
them moisture is obtained during the dry period. 
There are several genera (Camponotus, Myrmeco- 
cystus, Melophorus) in which this habit has been 
developed, and they are found both in the American 
and Australian deserts. 

It is natural that, just as the insects are most 
numerous in the clement spring and temperate 
autumn, so they are much more numerous in a 
season following good spring rains and a normal 
flood than in a year in which moisture and therefore 
annual flowers have been deficient. In this connec- 
tion the enormous variations from the normal which 
characterize the annual rainfall of deserts (pages 11- 
13) will be remembered. If the regular winter rains 
are deficient the annual plants and the butterflies, 
bees, and other insects are scarce as regards indivi- 
duals ; apparently also certain species are entirely 
absent, at any rate they are so rare that they are 
not detected. The possibility that insects and plants 
can " carry over " an unfavourable period not of 
months but of years requires investigation, but 
there is a good deal of evidence to suggest that it 
may indeed be so. For instance, Hartert was in 
the country south of Biskra, Algerian Sahara, in 
1908 and 1909 : he noticed white butterflies very 
rarely between Biskra and Borj Saada, and none 
between Borj Saada and Tuggurt. In 1912, after 



ANIMALS— PHYSICAL ENVIRONMENT 73 

good winter rains, he travelled along the same road, 
at the same season. He saw dozens of white 
butterflies between Biskra and Borj Saada, and 
hundreds of Melitaea and Euchloe between that place 
and Tuggurt. 

Spencer's observations upon the small mammals 
and other creatures of Central Australia, and the 
effect upon them of " good " and " bad " years, are 
extremely interesting. After the wet season the 
reproduction of the small rodents and marsupials 
is at its height ; the succeeding drought kills a very 
large number of them, especially the immature 
individuals, and the few survivors attain maturity 
without attaining the dimensions of individuals 
reared under more favourable conditions ; for 
instance, the adult males of the marsupial Phascogale 
cristicauda may vary in length from 136 to 220 
millimetres, and females carrying young from 125 to 
170 millimetres. A succession of dry years not only 
greatly reduces the numbers of small mammals, but 
also reduces their powers of reproduction. Thus 
the small, mouse-like marsupial Sminthopsis crassi- 
caudata, which has typically ten nipples, produces 
ten young at a birth in seasons of plenty, and not 
more than four or five in seasons of scarcity. " If 
the drought be abnormally prolonged then even the 
hardiest animals will suffer, and the fauna wiU be 
so reduced that it may take some time before 
increased fertility on the part of the survivors and 
the influx of immigrants from the broad belt of land 
enclosing the central region will make good the 
deficiency " (Spencer). 



74 ANIMAL LIFE IN DESERTS 

The effects of good rain upon bird life is illustrated 
by Ticehurst's observation that the White-cheeked 
Bulbul {Pycnonotus I. leucotis) of Sind, which normally 
breeds in March and April, breeds again in Sep- 
tember in years in which much rain has fallen. 
The fact that this bird is a denizen rather of thickets 
and gardens than of the bare desert does not render 
it unsuitable for inclusion in our study of the biology 
of deserts, for the conditions of cUmate and the 
variations between " good " and " bad " years are 
essentially the same in the desert as in the oasis. 
It seems that this observation and Spencer's upon 
the small marsupials are best included here rather 
than in the section which deals expressly with water, 
because quite clearly the increased reproduction of 
bird or marsupial is not to be ascribed directly to the 
rainfall but to some much more general effect of 
the rainfall upon vegetation, insects, etc., and so 
indirectly upon the larger creatures. 

The present is a convenient place for considering 
a remarkable type of small mammal which has 
been evolved repeatedly in deserts and semi-deserts, 
and not in any other environment : as we are 
ignorant of the causes which have contributed to 
the production of this type it appears best to group 
it with other general relationships with the physical 
environment. The mammalian type to which I 
refer is most familiar to us in the Jerboa (Fig. 31). 
This is a rodent about the size of a rat, provided 
with short f ore-Umbs, which are not remarkable, and 
excessively long hind-legs and long, narrow feet ; 
the toes are reduced in number to two ; the tail 



ANIMALS— PHYSICAL ENVIRONMENT 75 

is very long, covered with short hairs, and bearing 
at its tip a large tuft. The short fore-Umbs are 
used for burrowing, holding food, and apparently 
also for lifting water to the mouth (page 90) : 
the length of the hind-limbs is correlated with the 
habit of progressing by leaping and not by running, 
and it is possible that they serve also to give the 
Jerboa and the animals which resemble it an in- 




Fig. 31. Hairy-footed Jerboa {Jaculus jaculus) from Egypt. 

Notice the long hind-legs with reduced number of toes, and the long tail^with a terminal 
tuft of hair, and the biped attitude. (Draum from life by Miss A. M. Gayton.) 

creased power of observing the approach of enemies 
on the bare ground. The speed which a Jerboa 
can attain by jumping, and the great irregularity 
of its movements, undoubtedly make it extremely 
difficult to capture, a fact which can be verified if 
you liberate a Jerboa in the confined space of a 
room and endeavour to catch it in a butterfly net. 
The Jerboas (Dipus and Jaculus) belong to the 
Dipodidse, a family of Rodentia of which all the 



76 



ANIMAL LIFE IN DESERTS 



members are modified in the same direction as the 
Jerboa, though not all to the same extent. In 
AUactaga, for instance, five toes are present on the 
hind-foot, though two are vestigial ; in Scarturus 
the first digit is absent, and the fifth vestigial ; in 
Dipus and Jaculus only three toes are present, 
and the two which are lacking are not represented 
by any vestige externally (Fig. 32). 





Fig. 32. — UNDER'SURrACE or Right Foot of Allactaga indica {A), Scar- 
turus tetradactyla {B), and Jaculus jaculus (C). 
{After R. I. Pocock.) 

These genera are characteristic of the Great 
Palaearctic Desert and of the steppes on its fringe ; 
the closely related Zapus is American, and is inter- 
esting because it is intermediate in habit and 
anatomy between the ordinary running quadruped 
mice and the biped jumping Jerboas. In another 



ANIMALS— PHYSICAL ENVIRONMENT 77 

family of rodents, the Muridae, the same modifica- 
tion of form may be seen in desert species belonging 
to two of the sub-famiUes. Of the first, the Ger- 
billinae, or Gerbils ^ (Fig. 33), no member has be- 
come completely biped, but nearly all the genera 
and species show some lengthening of the hind-leg 
and hind-foot and tend to progress at times by 
running, at others by leaping. The species figured 




Fig. 33. — East African Gerbil {Taterona mcina) from East Africa. 

This animal is typical of a very large number of species, most of which are found in various 
parts of the Great Palaearctic Desert. (Drawn from life by Miss A. M. Gayton,) 

(Taterona vicina) shows these characteristics well, 
and is drawn from life in a characteristic biped 
attitude. Other Gerbils (e.g. Meriones) are more 
rat-Hke in form and in habit. In the second sub- 
family, the Murinse or True Mice, occur Conilurus 
and Notomys in the Australian deserts, exhibiting 
various stages in the lengthening of legs and feet 

^Examples are Meriones (pages 92, 130, etc.), Gerbillus 
(page 138), and Dipodillus (pages 103, 127). 



78 ANIMAL LIFE IN DESERTS 

and the assumption of the biped habit. In the 
deserts of the southern part of North America 
animals resembling Jerboas have been evolved 
from yet another family of rodents, the Hetero- 
myidae. 

The rodents which have already been mentioned 
all belong to the section Myomorpha ; in another 
section, the Hystricomorpha, and not closely related 
to the forms which have been considered, is the 
Cape Jumping Hare (Pedetes). This animal is 
much larger than any Jerboa, but resembles that 
animal in its long hind-legs and long tail : it feeds 
on all fours, but when it is pursued it escapes by 
prodigious leaps. It lives in arid and desert places 
in Africa from Mozambique southwards. 

It is surprising to find similar " Jerboa-like " 
animals among the totally imrelated marsupials : 
good examples are Phascogale Hillieri and Ante- 
chinomys. The last lives in Central Australia in 
sandy plains among tussocks of grass in the same 
environment as the rodents Conilurus and Mus 
gouldi. The Antechinomys and Conilurus are Jer* 
boa-like, progress by jumping, and show remarkable 
general similarity in form ; the Mus, which is equally 
common, and apparently quite as successful in the 
business of life, is an ordinary mouse, and pro- 
gresses by running : it is difficult to see why the 
jumping habit has been evolved in the Conilurus 
and Antechinomys unless, as Spencer suggests, the 
resultant irregularity in movement tends to baffle 
small hawks chasing them. Conilm*us is an ex- 
tremely abundant rodent ; Antechinomys, which 



ANIMALS— PHYSICAL ENVIRONMENT 79 

so closely resembles it in habits and shape, is very- 
rare, possibly because it is an insect-eater (page 83). 
Every one of these small Jerboa-like creatm*es 
exhibits the coloration typical of so many desert 
animals (page 141), the sandy, unicolorous upper 
surface, and white belly. 

For the following tables I am indebted to the 
kindness of Mr. O. Thomas, F.R.S., of the British 
Museum (Natural History). The first makes clear 
the relationships of the forms of which I have 
been speaking ; it shows that animals outwardly 
resembling the Jerboa have been evolved on a 
number of different occasions, apparently as a 
response to the conditions of life in a desert, and 
that in each continent the Jerboa-like animal has 
been produced from a different family or sub- 
family. 



Order. 


Section. 


Family. 


Sub-family. 


Genus. 


Habitat. 


Rodentia 


Myomorpha 


DlpodldsB 


Dlpodlnae 


AUactaga 

Dipua 

Jaculus 


Great Pate- 
arctic Des- 
ert 


» 


,, 


,, 


Zapodinse 


Zapus 


America 


»> 


" 


Murldse 


MurinsB 


Conilunis 
Notomys 


Australia 


.. 


i> 


" 


GerbllUnsa 


Gerbillus 
Meriones 
DipodiUus 


Great Pate- 
arctic Des- 
ert 


• 


•> 


Heteromyid» 




Dlpodomys 
Perognathua 


America 


>» 


Hystrlcomorpha 


PedetldsB 




Pedetes 


S. Africa 


MareupiaUa . 


Polyprotodontla 


DaayuridsB 


DasyurlnsB 


Antechlnomys 
Phascogale 


Australia 



The second table shows at a glance the number 
of toes present in these Jerboa-Hke animals, and 
emphasizes the fact that a reduction in the number 
of toes has repeatedly taken place. Five is of 



80 



ANIMAL LIFE IN DESERTS 



course the full number of digits in either the fore- 
or the hind-foot. " 4 and 1 " or " 3 and 2 " indi- 
cate that 4 (or 3) normal digits are present and 1 
(or 2) which is reduced in size. Toes are only 
shown as " vestigial " when they are minute, and 
probably not used : thus Perognathus has five 
digits on the hand, of which one is small : on the 
foot it has either three normal toes and two small 
ones, or else (in another species) three normal toes, 
one small and one vestigial. A zero in the " ves- 
tigial " column indicates that no external trace of 
digit can be found. In Dipus and Jaculus the 
reduction has gone so far that two toes are not 
even represented by a vestige. 



Genus. 



Dipus, Jaculus . 

Scarturus 

AUactaga 

Gerbillus 

Zapus 

Perognathus, either 

or 
Conilurus 
Notomys ... 
Antechinomys 
Phascogale hillieri 
Pedetes . 



Number of Toes. 



Fore -foot. 



4 & 



Hind-foot. 



Functional. Vestigial, 



CHAPTER V 

ANIMALS AND THE PHYSICAL 
ENVIRONMENT (continued) 

i. Water Supplies, ii. Fauna of Waters in Deserts, iii. 
Heat and Relative Humidity, iv. Animals and Wind. v. 
Relationships with Soil. 

i. Water Supplies 

I propose to marshal some of the available facts 
which relate to the reaction of the desert animals 
to drought, heat, wind, and other particular ele- 
ments in the cHmate, and to deal first with the 
means adopted by the animals for making the 
most of a scanty and irregular water supply. In 
many semi-deserts and in all deserts rain falls 
at such rare intervals that life would be impos- 
sible to any species directly and solely dependent 
on it, but other sources of water are available, 
and probably on the whole more important. Per- 
haps the most obvious is the dew. Meteorological 
records of dew-fall are scanty from all parts of the 
world, and observation of dew-drinking by small 
animals are very few. Atkinson, writing of his 
experiences at Abu Kir in Egypt, remarks : " The 
water supply of the numerous beetles inhabiting 
the patches of baked clay in the coastal deserts 

81 o 



82 ANIMAL LIFE IN DESERTS 

was a puzzle to the writer till it was noticed that 
they drank drops of dew from the angles of dried- 
up thorny plants." 

Though lack of precise observation prevents us 
from forming a clear idea of the importance of dew 
to the fauna, it is probably considerable, at any 
rate at certain seasons. A more constant source 
of supply is the desert vegetation. Plants, however 
dead they are, and however long they have been 
exposed to the desert wind and sun, are not chemi- 
cally dry, any more than hay or chaff are dry. 
It has also been suggested that during digestion 
by an animal a certain additional amount of water 
may be elaborated as a by-product of the break- 
down of the complex chemical bodies of which the 
plant consists. 

One can therefore understand that it is possible 
for a seed-eating mammal or bird to exist for long 
periods without eating succulent plants or drinking 
the dew or obtaining water from any visible source, 
and some of them can do this. I remember an 
Egyptian Jerboa which was kept by a member of 
my family as a pet. It was given no water and 
lived for many months on crushed oats and bran ; 
when it was offered apple or carrot or other moist 
food it generally refused to eat it. That it could 
not drink dew is certain because it Hved in a London 
house. It is almost certain that many birds, in- 
sects, and small mammals depend solely upon the 
minute quantities of water to be found in seeds 
and dead plants which have become completely 
" air-dry." 



ANIMALS— PHYSICAL ENVIRONMENT 83 

It is reasonable to suppose that just as some 
animals obtain their small requirements of water 
from the plants they eat, so others obtain their 
supply from the ants, grasshoppers, etc., which are 
their staple food : such cases are probably few be- 
cause animals which are dependent upon insects for 
their food and drink are uncommon in aU deserts : 
this applies not only to the order Insectivora but 
also to insect-eating members of other orders. 
This rarity is due in all probabiHty to the great 
seasonal fluctuation which occurs in the number 
of insects, and that in turn follows the enormous 
variations in climate to which all deserts are sub- 
ject. In the Great Palsearctic Desert I know of 
no purely insectivorous ^ mammal, except the bats. 
Of the food of such resident birds as the Desert 
Warbler {Sylvia nana), which is probably a pure 
insectivora, we have no accurate information. In 
the Australian deserts the ants are a dominant 
group : it appears that they are the staple food of 
Myrmecobius, a marsupial ant-eater, which devours 
them above ground, and of Notoryctes, the marsupial 
mole, which lives beneath the surface. 

Actual water-holes, springs, rivers, etc., provide 
water to the creatures which live on their banks, 
and to a number of others which come in from the 
surrounding deserts to drink. Among them are 
many birds, and bats, a few insects, and many 
large terrestrial mammals. 

^The hedgehogs which inhabit many parts of this area (e.g. 
Hemiechinus auritus), though '* Insectivora " in the technical 
sense, are not an exception to this statement, for they are by 
no means exclusively eaters of insects. 



84 ANIMAL LIFE IN DESERTS 

Among birds which fly to water the most remark- 
able are the Sandgrouse (Fig. 34). Sportsmen are 
aware that-ithe various species of S andgrous e 
(Pterocles and other gener a),jKh igtrt fiKabit nearly 
J every part of th e Great Palsearc ticjesert water 
hff at certain spots on the banks^ of rivers, at certain 
' regular "EourS. There is good evidence that the 
birds fly in from very many miles, and as the chosen 
watering-place is often very circumscribed, immense 
numbers of birds congregate there for a very short 
period every day. Different species of Sandgrouse 
water at different times of day, the majority in 
the early morning, Lichtenstein's Sandgrouse before 
sunrise, or even in the middle of the night when 
there is moonUght. / Sandgrouse normally stand in 
jW shallow water when drinking, and as their legs are 
short their breasts become saturated with water.if 
This is true of both sexes and happens at all sea- 
sons. It is reasonable to suppose that from this 
has developed their very remarkable manner of 
supplying water to their chicks. Native hunters 
have always asserted that they carry water to their 
young in the hot, bare desert in their saturated 
breast plumage. That this is correct has been 
proved by Meade-Waldo, who has had many broods 
of Sandgrouse (fifty-one of Pterocles alcatus, seven 
of P. exustus, and three of P. arenarius) hatched in 
his aviaries. /The young feed themselves on small 
y, seeds^from the time of their emergence from the 
i/" egg, and are attended by both parents. " The 
male rubs his breast violently up and down on the 
ground — a, motion quite distinct from dustmg, — and 




bO 

S 



ANIMALS— PHYSICAL ENVIRONMENT 85 

when his feathers are awry gets into his drinking- 
water and saturates the feathers of his underparts. 
When soaked he goes through the motion of flying 
away, nodding his head, etc. ; then, rememberng 
his family is close by, he would run to the hen, 
make a demonstration, when the young run out, 
get under him, and suck the water from his breast 
— ^the appearance being that of a mammal suckling 
her young. / The young pass the feathers through 
their bills, and keep changing places until the supply l^ 
becomes exhausted. Until the young can fly they 
take water in no other way, and the cock gives it 
to the young only.^"" (Meade- Waldo.) As soon as 
the chicks can fly they cease entirely to drink from 
the males' breast-feathers./ Sandgrouse in nature 
breed at various dates, but one may say roughly 
that they choose the hot weather. The following 
are dates on which eggs of certain species have been 
found in various places : 



Western Pintailed 


May 


Spain. 


Sandgrouse 






Eastern Pintailed 


May, June, July 


Mesopo- 


Sandgrouse 




tamia 


Spotted Sandgrouse 


April, May, June, 


Mesopo- 




July 


tamia 


Little Pintailed 


Throughout the 


Punjab. 


Sandgrouse 


year, especially 
March to July 




Pallas' Sandgrouse 


March to June 


Central 
Asia. 



It seems that many young Sandgrouse are brought 



86 ANIMAL LIFE IN DESERTS 

into the world when the air is hot and dry, when 
the desert soil is so hot that you cannot keep your 
hand on it, and when the vegetation is parched 
and the seeds on which they feed are already air- 
dry. They run about, even during the hot hoiu-s, 
near their parents but not sheltered by them, as 
I have myseK seen at MandaH on the Perso-Mesopo- 
tamian frontier in August. ^ As their only means 
of maintaining a body temperature of about 100° F. 
while they run in a dry atmosphere on desert, 
the surface of which is 150° F. or higher, is by evapor- 
ating water, it is not remarkable that special methods 
have been evolved to bring water to them in their 
waterless home. /What is remarkable is that the 
other desert birds appear to Uve successfully without 
watering their chicks at all. The Crested Larks 
(Galerida cristata and G. thehloe) fly regularly to 
water in the evening when water is available near 
their haunts, though there is no evidence that this 
habit is invariable or obHgatory ; the Stone Curlew 
{(Edicnemus) and Coursers {Cursorius) do the same, 
at any rate sometimes. 

Ticehurst, writing of the birds of Sind, states that 
the Trumpeter Bullfinch (Erythrospiza githagineus 
crassirostris) drinks nearly every hour, and that 
the Striated Bunting (Emheriza s. striolata) drinks 
at frequent intervals during the day. So far as 
we know none of the small desert birds give water 
to their young by regurgitation, and certainly 
none carry water in their breast-feathers. There 
is a group of birds which seem to be entirely inde- 
pendent of water, or rather to depend solely on 



ANIMALS— PHYSICAL ENVIRONMENT 87 

the water which they can obtain from dew, insects, 
and the vegetation ; in this group fall the Houbara 
Bustard (Chlamydotis undulata), the Chough Thrushes 
(Podoces), the Larks Alsemon and Ammomanes, and 
others. 

Certain birds inhabit the fringe of deserts, but 
seem to be prevented from penetrating them because 
they cannot dispense with drinking. The need for 
a drink of water is in these cases a Hmiting factor 
in their distribution. An excellent example is the 
Black Partridge (FrancoUnus vulgaris), an abundant 
bird in the Mesopotamian plain. It is never found 
more than a couple of hundred yards from water ; 
it is a lover of thick scrub, but where scrub occurs 
far from water the Black Partridge cannot be found. 
In California a somewhat similar case occurs. The 
Desert Quail {Lophortyx gambeli) wanders out into 
the desert to forage, but its real home is] in the 
scrub along the banks of ^the California River : 
it requires to drink every morning and evening. 

It is difficult to study the habits of bats. Cer- 
tainly many desert-dweUing species visit water 
regularly at the beginiy^ng of their evening flight, 
but we have no reason to say that this is the custom 
of desert bats in general. 

Many wasps and other Hymenoptera make long 
flights to drink, and crowd any spot at which they 
can obtain water : some species require also mud 
for nest-building. In Mesopotamia one often ob- 
served the Oriental Hornet {Vespa orientalis) drink- 
ing greedily in mess-rooms, and drowning itself 
in drinking-cups : this had a considerable hygienic 



88 ANIMAL LIFE IN DESERTS 

importance, for the hornet was a filthy feeder and 
was frequently loaded with bacteria derived from 
the human intestine. 

Among the large mammaHa there are many species 
which drink, and drink freely, when an opportunity 
is given them, but which are able to dispense with 
drinking when it is necessary. They derive a 
considerable quantity of water from the vegetation 
which they eat, and one need hardly say that the 
amount of vegetation, and of moisture in it, varies 
very greatly with the season. Thus Doughty ob- 
served in Arabia that " the camels now feeding in 
the sappy rabbia (spring pasturage) were jezzin or 
'not drinking.' In good spring years they are 
in these diras almost two and a haK months jezzin, 
and are not driven to the watering." Gregory 
quotes very similar facts from Australia : he says 
that in 1891 Tietkin marched 537 miles in thirty-four 
days without watering his camels, and that PhilUpson 
kept a herd without water in a sand-hill country 
for two months. On the other hand, if very httle 
grazing, or none at all, can be obtained and if camels 
are doing hard work, their endurance is very much 
less. Augieras speaks of sixteen days' march without 
water in the Central Sahara as a severe trial to his 
camels, and Haywood gives one to understand that 
about eight days is near the camel's Hmit in mid- 
summer in Tanezruft, a district of the Sahara which 
at that season is entirely devoid of any grazing. 
Camels not only possess this remarkable power of 
abstaining from drinking for long periods, but they 
are able to drink salt and bitter water which man 



ANIMALS— PHYSICAL ENVIRONMENT 89 

and horses cannot swallow ; when water is available 
their consumption is low, about seven gallons daily 
compared with the horse's thirty. Other large 
creatures which are able to dispense with drinking, 
but which drink when they have opportimity, are 
the ostrich, the giraffe, the eland, and probably 
many other antelopes from the parts of tropical 
Africa which are rather semi-arid grass-land than 
desert. 

In desert of an extreme tjrpe many of the animals 
have perforce to dispense entirely with drinking 
water, and it appears that a certain number of 
species never drink at all, and derive their whole 
water-supply from the desert herbage, and possibly 
the dew. In this category of total abstainers Abel 
Chapman mentions the Addax (Fig. 35) and Oryx 
(Fig. 36) antelopes and the Addra and Sudan 
gazelles, all of them inhabitants of the Anglo- 
Egyptian Sudan. He also states that on certain 
small islands in the Red Sea Gazella arahica exists 
as a dwarf race, not exceeding one-third of the 
weight of the normal race, and that these islands 
are entirely without water. 

It is probable that this abiUty to dispense with 
water is a character of many of the gazelles (Fig. 37), 
and that it accounts for the fact that species of the 
genus are found almost throughout the Great 
Palsearctic Desert. 

Grinnell and Dixon state that the Round-tailed 
Ground Squirrel {Citellus tereticaudus) does not drink 
even when it has the opportunity ; another species, 
the Desert Antelope Ground Squirrel (Ammospermo- 



90 



ANIMAL LIFE IN DESERTS 



philus leucurus), can last for several months between 
drinks, but does drink, in nature, when water is 
available. We know almost nothing of the water 
needs of our Old World rodents. I have already 
recounted observations made on a captive Egyptian 




Fig. 35. — Addax Antelope (Addax nasomaculatus), Male, from the 

Sudan. 

{Drawn from life by Miss A. M. Gayton.) 



Jerboa in London : Cheeseman kept captive speci- 
mens of a different species (Jaculus loftusi) in Basra, 
Mesopotamia, in summer, and remarked that " they 
drank frequently, taking small sips in their f orepaws. 
This is remarkable, as their earths are often placed 




Fig. 36. — Arabian Oryx {Oryx leucoryx), an Inhabitant of Waterless 

Sandy Desert. 

{Drawn from life by Miss A. M. Gayton.) 




Fig. 37. — Persian Gazelle {GazelJa subgutturosa), from Kirkuk, Perso- 

Mesopotamian Frontier. 

(Dream from life by Miss A. M. Gayton.) 

91 



92 ANIMAL LIFE IN DESERTS 

where both dew and water would be to all appear- 
ances unobtainable." Probably, therefore, this Jer- 
boa is to be grouped with the animals which do 
drink, but need not do so. The Gerbil Meriones 
swinhoeii, from the flat stony uplands of the Afghan 
Border, refuses water in captivity (C. M. Ingoldby). 

According to Camp, most American desert reptiles 
require no water, and this must be true of many 
which occur in the Great Palaearctic Desert : my 
correspondent, Capt. G. W. G. Kingston, suppUes a 
good example in the Agama, which frequents the 
ruins of Ur of the Chaldees in Southern Mesopotamia, 
a dusty spot far from the River Euphrates or any 
well, and without rain or vegetation for at least 
seven months in the year. The lizard Moloch 
horridus of West and South Australia, a repulsive 
animal covered with tubercles and spines, has the 
power of absorbing water through the skin after a 
fall of rain. The Gecko (Eublepharis macularis), 
which occurs in Persia and North-west India, 
drinks freely from a saucer in captivity (C. M. 
Ingoldby). 

As our knowledge of the biology of the smaller 
forms of desert Ufe increases we shall no doubt find 
remarkable instances of abiUty to exist without 
moisture. The case of a Stratiomyid fly {Hermetia 
chrysophila), the larvae of which are able to endure 
at least fifteen months without food or water, and 
which eat decayed cactus joints whenever moisture 
is present, is probably typical of a large number of 
other insects. 



ANIMALS— PHYSICAL ENVIRONMENT 93 

ii. Fauna op Waters in Deserts 

Conditions of life in a permanent well or spring 
in the desert, or in a river which runs for part of its 
course through desert, are not in any way different 
from those which prevail in similar situations 
elsewhere, and the animals of these springs and rivers 
do not concern us. But there are other and more 
temporary water-places in deserts, and those of 
them which are liable to be filled with water at 
fairly regular intervals support a very interesting 
fauna. 

The inhabitants of the temporary pools are exposed 
either to death or else to the full rigour of the desert 
climate for many months on end, while the pools 
are dry ; and even when they are j&Ued with water 
the position of the animals is precarious, because the 
period which they will be able to devote to active 
life, to feeding and to reproduction, is a short one. 
Moreover, during the gradual drying up of their 
pool the saltness of the water increases : so that the 
animals are faced with three separate problems — the 
ordinary problems of Hf e in fresh water, the gradually 
increasing salinity of their water, and its eventual 
disappearance. 

Certain groups of animals, abundant in the fresh 
water of other climates, are entirely unable to solve 
these problems. The Newts, for instance, are found 
all over Northern Europe and Asia, but they are 
limited in a southward direction by the northern 
edge of the Great Palsearctic Desert, and no newt 
appears to have penetrated or crossed it. It would 



94 ANIMAL LIFE IN DESERTS 

be interesting to study the effect of belts of desert 
upon the distribution of leeches, planarians, and 
other naked damp-skinned animals. 

Other animals are unable to survive the desicca- 
tion, but become temporary colonists of water-holes 
in deserts and when the water dries up are locally 
exterminated. Among them are denizens of per- 
manent waters, which are occasionally introduced 
into a temporary pool by floods ; this is an accident 
of common occurrence to small fish, and doubtless 
to a large number of other forms of life. Winged 
insects also, whose early stages are passed in waters, 
frequently colonize these temporary pools. This 
temporary colonization is of course most commonly 
seen in parts of the desert close to permanent pools 
or rivers : temporary pools in such places are 
invaded by many forms of gnats and mosquitoes, 
by gad-flies (Tabanidse) and by dragon-flies. It is 
probable that the Tabanidae and dragon-flies seldom 
pass successfully through their early stages, which 
are of long duration ; but the gnats and mosquitoes 
frequently pass rapidly through several generations. 
As the pool shrinks in size and increases in saltness 
it becomes a fit home for the larvae of small fhes of 
the family Ephydridae, and these are sometimes 
present in enormous numbers. 

But it is the permanent inhabitants of these 
temporary pools which are most interesting, because 
their methods of solving the problems which confront 
them are so varied. The Phyllopod Crustacea 
(e.g. Apus and Estheria) exist through the drought 
as eggs, and can survive a period of drying which 



ANIMALS— PHYSICAL ENVIRONMENT 95 

extends over years. Recurring periods of drought 
are necessary for their existence, so that it is not 
remarkable that they should be found in deserts 
and semi-deserts in nearly every part of the globe. 
One member of this group, the Brine Shrimp 
(Artemia), is not only extremely resistant to drought 
in the egg stage, but also requires for its development 
water nearly or quite saturated with salt ; and it is 
found in temporary salt pools in many parts of the 
world, both in deserts and other situations. Certain 
Phyllopods are capable of extremely rapid growth 
when the mud in which their eggs have been dormant 
is flooded, and when the shallow pool is heated by a 
desert sun. Spencer records that Apus in Central 
Australia reaches a length of 2^ inches in fourteen 
days after rain falls. 

Other inhabitants of temporary pools descend into 
the mud when the pool dries up, and there continue 
to exist. Examples are the crab (Telphusa) and 
crayfish (Astacopsis) of Central AustraHa, and many 
water-beetles and molluscs. Of the Gasteropod 
molluscs many are protected by an operculum, with 
which to close the mouth of the shell : Isidorella 
newcombi, in water-holes in Central Australia, plugs 
the shell with mud, which is probably specially 
prepared by passage through the ahmentary canal. 

The biology of the frogs found by the Horn 
Expedition to Central Australia has been treated 
at some length by Spencer. Among the species 
collected were some which showed marked abiUty 
to breed rapidly and take advantage of a short 
favourable period, and others whose habits enabled 



96 ANIMAL LIFE IN DESERTS 

them to survive drought in a remarkable manner. 

That frogs are able to exist at all in temporary 
waters in Central Australia is very remarkable, 
because their need for water is great, and their 
damp skins are entirely unsuited to Ufe in a dry 
atmosphere, in which they invariably die. Six 
species were found in the desert region, but two 
were rare and little was discovered about their 
habits. The remaining four all showed different 
interesting methods of overcoming the hostiUty of 
their environment. They were all of them able to 
spawn at any time of year, as soon as rain had fallen. 

Hyla rubella^ a close relative of the green Treefrog 
of Southern Europe, was found in nearly every 
water-hole which was visited during the dry season. 
It appears that it does not burrow in damp soil, 
and therefore when its water-hole dries up it perishes. 
On the other hand, it is a very rapid breeder, and if 
rain falls heavily its tadpoles are carried down the 
channels and its range is, for the moment, very 
greatly increased. It is therefore a species which 
depends for its success in colonizing Central AustraUa 
on its abiHty to produce its young rapidly and in 
large numbers : it might be said to be successful 
because its high birth-rate after rain exceeds its 
high death-rate diu-ing the dry weather. If the 
drought exterminates a colony of this frog at a 
certain water-hole in the bed of a stream, the next 
flood will enable the species to colonize the same 
spot once again from a permanent pool. 

Another common frog was Limnodynastes ornatus. 
Like many of the frogs of the more arid parts of 



ANIMALS— PHYSICAL ENVIRONMENT 97 

Australia this species is able to excavate burrows in 
soft soil. These it makes in sandy places in the 
beds of temporary streams, and it reaches a layer of 
damp sand even though the stream has been dry 
for a long time. The burrows are not permanent ; 
a fresh one is made for each day, and at night, when 
the temperature is low and the humidity high, the 
animal ascends to the surface to hunt for beetles. 

Heleioporus pictus is another burrowing form, but 
it makes permanent burrows. In these it exists 
for months at a stretch during periods of drought, 
I am informed that the eggs are laid in the burrow, 
about 18 inches deep in the sand, in a foamy mass. 
Development occurs in the egg to such a stage that 
the tadpole is ready to emerge as soon as rain faUs. 
The albumen of the egg is hygroscopic, and when 
moisture is abundant it is absorbed in such quantities 
as to burst the membrane which covers the egg, and 
release the tadpole. 

Chiroleptes platycephalus resembles the last species 
in making a permanent burrow and in its abiHty to 
exist in it through a long period of drought. It 
possesses also remarkable powers of storing water, 
and it can contain a very considerable quantity in 
its urinary bladder, subcutaneous tissues, and peri- 
toneal cavity ; when it is fully charged with water 
it is almost spherical. It makes permanent burrows 
to the depth of about a foot in soil which will shortly 
be baked by the sun into a mass of hard clay, and 
here it remains for the dry season. By means of 
its burrowing and its powers of storing fluid it is 
able to resist long droughts ; permanent springs and 



98 ANIMAL LIFE IN DESERTS 

pools are unsuited to it, and it is only found in places 
in which it will be exposed to desiccation periodically. 
This animal can contain so much fluid that it is 
occasionally used by the Australian aborigine as a 
source of drinking-water. It appears to imbibe the J 
water through its skin, as weU as its mouth, and to 
do so very rapidly ; an AustraUan friend, Mr. L. 
Harrison, writes to me that if you " put a lean, dry, 
herring-gutted Chiroleptes into a beaker with 2 inches 
of water, in two minutes your frog resembles a 
somewhat knobly tennis-ball." 

iii. Heat and Relative Humidity 

These two factors must be considered together 
because under natural conditions a high temperature 
and a low relative humidity are generally associated 
(page 23). It is not therefore possible, in the 
absence of experimental work, to discriminate 
between the effects of the two. 

The very existence of small animals on the surface 
of the desert at midday is remarkable. Most of 
these animals — for example, the Hzards and beetles 
— are cold-blooded, so that one supposes that their 
temperatures approximate to that of the air in 
which they find themselves at any given time ; 
and as they are relatively small the fluctuations of 
their internal temperatures must be rapid. In 
spite of this, animals do manage to exist on the 
desert soil even in the middle of the day in summer. 

Good examples among the reptiles are the Agama 
lizard at Ur of the Chaldees, to which reference has 
been made (page 92), and the Chuckwalla (Sauro- 



ANIMALS— PHYSICAL ENVIRONMENT 99 

malus), a vegetarian lizard of the Calif ornian deserts 
which sits upon rocks when they are too hot for 
the hand to touch (Camp). 

Many insects have the same power of Hving on 
the surface of the soil at midday, even during the 
hottest season. On June 2, 1922, I observed at 
Jericho, Palestine, at noon that the shade tem- 
perature was 90° F. (32-3° C), and the surface of 
the hard clay soil 124° F. (50-8° C), and on it two 
species of mantis larvae (Eremiaphila and Fischeria), 
and adults of a Short-horned Grasshopper, were 
moving about. In deserts nearer the Equator 
much greater surface temperatures (page 21) are 
attained, but these figures serve to show the degree 
of heat to which the insects, etc., are exposed on 
the bare desert. 

The case of the diurnal mammaha of the desert 
is very different, and their survival of summer 
midday conditions is not so remarkable. Such 
animals as hares, gazelles, and camels are large, so 
that in any case they would not be exposed to 
very rapid fluctuations of internal temperature : 
they are, moreover, warm-blooded, that is to say, 
provided with a mechanism which maintains their 
bodies at or near a constant temperature : there- 
fore fluctuation of air temperature affects a gazelle 
or camel, or even a hare, very much less than it 
affects a Hzard or beetle; so that the power of 
j the mammals to survive the midday heat is less 
i remarkable than their ability to provide themselves 
I with water, by the evaporation of some of which 
! they maintain their "normal temperature." 



100 ANIMAL LIFE IN DESERTS 

On the other hand, to many desert-dwellers ex- 
posure to the climate at midday is very rapidly 
fatal. The Horn Expedition to Central Australia 
observed that if the hzard Tiliqua was taken from 
its hole and put on the sand at noon it ran a few 
yards and rolled over dead, and similar examples 
might be multipHed. The animals which are unable 
to survive surface conditions at midday resort to 
various devices in order to reach a more equable 
temperature and humidity than is prevalent in the 
open air. A few birds obtain all the shelter they 
require by getting into the centre of trees and bushes. 
Thus in the plain of Jericho the Great Grey Shrike 
{Lanius excuhitor aucheri) and the black and white 
Wheatear {Saxicola lugens) take refuge during the 
heat of the day in midsummer in the bottoms of 
bushes of Atriplex and Zizyphus (Fig. 25). At all 
other times they are most conspicuous birds, the 
Shrike perched on the top of a Zizyphus, and the 
Wheatear in any unprotected position. In a similar 
way one may observe House Sparrows {Passer 
domesticus hiblicus) and White-cheeked Bulbuls {Pyc- 
nonotus leucotis mesopotamice) bury themselves during 
summer days at Basra in the dense mass of leaf- 
bases and young shoots which spring from the 
crown of a date-palm. 

Many small animals take refuge under stones and 
in similar places, particularly at the seasons when 
traces of moisture are still present. In the Great 
Palaearctic Desert, wherever mixed stones and earth 
occur (page 47), a large collection of small animals 
may be obtained by turning over stones during the 



I 



ANIMALS— PHYSICAL ENVIRONMENT 101 

spring and early summer. One obtains such crea- 
tures as woodlice ; millipedes and centipedes ; 
spiders, scorpions, mites and pseudo-scorpions ; 
lepismids, Japyx, earwigs, cockroaches, crickets, 
very numerous beetles, bugs, ants ; snails and 
occasionally slugs, and earthworms. What befalls 
these animals in the hot and dry season is largely 
a matter of conjecture. Probably some descend 
deep into cracks in the soil, and others aestivate 
in the egg and possibly in other stages. Spencer 
attributed the existence of land-snails in Central 
AustraUa to various factors in different species. 
Some existed on the shady side of hills, others 
sestivated among tree roots, others closed the mouth 
of the shell with a plug of mud ; others again were 
minute and descended deeply into the clefts in 
the soil. It is at any rate certain that the rich 
fauna that one finds under stones in Persia, Pales- 
tine, Algeria, and other stony deserts, in spring- 
time is almost as ephemeral as the annual flowers, 
and it is very remarkable that such moisture- 
loving forms as snails and earthworms should be 
able to exist through the summer in any stage in 
these countries. 

The geographical distribution within the Great 
Palaearctic Desert of these multitudes of smaU 
creatures depends among other factors on the 
presence of stones under which to shelter, and of 
regularly recurring rainfall, but a very similar associa- 
tion may be found in Lower Mesopotamia, a stoneless 
plain consisting of nothing but the finest silt carried 
down by the Tigris and Euphrates ; in this country 



102 ANIMAL LIFE IN DESERTS 

a fauna is found after rain, between the trunk and 
the leaf -bases of the date palm ; this fauna is rela- 
tively rich and contains all the groups which I have 
just enumerated as characteristic of stone and earth 
desert in spring. In fact, one may say that the 
animals which shelter in the date-palm in Mesopo- 
tamia are the biological counterpart of those found 
under stones in Persia or Palestine. To what 
extent the same genera or species of animals are 
represented in both we do not at present know. 

Other animals which are unable to endure the 
climate of the surface of the desert dig burrows 
or use burrows which have been excavated by other 
creatures. They thus easily reach a zone in which 
temperature and humidity are nearly constant 
(page 22). In the group of active burrowers fall 
certain lizards and snakes, and nearly all the small 
rodents (Jerboas, Gerbils, Spiny Mice, and many 
others), and some at least of the small marsupials 
of Central AustraHa. Many observers have not" ed 
the extraordinary abiUty of the House Mouse (Mus 
musculus) and its very close relatives {Mus gentilis 
and other forms) to colonize human habitations 
in nearly every part of the Great Palaearctic Desert : 
the rapidity with which they become abundant in 
isolated camps in Mesopotamia was frequently 
noticed. These animals are protected from great 
fluctuations of heat and relative humidity by their 
burrows which are made beneath houses, and be- 
cause they frequently travel from place to place 
in boxes and bales. If they were diurnal and Uved 
openly in man's habitations they would be faced 



^ >» 




ANIMALS— PHYSICAL ENVIRONMENT 103 

with such fluctuation of temperature and humidity 
as might prevent their colonizing houses in the 
desert. 

Many of the small wild rodents close the mouths 
of their burrows by day with a plug of earth, and 
no doubt this tends still further to stabiHze the 
cUmatic conditions which prevail in the burrow. 
Detailed observations on this point are lacking for 
many species, but among rodents which plug the 
burrow one may mention Dipodillus dasyurus and 
Jaculus loftusi and Nesohia huxtoni in Mesopotamia, 
and the American genus Dipodops ; among those 
which leave the burrow open are Jaculus (species ?) 
in Palestine, and Dipodomys deserti (Fig. 38) in the 
American deserts. That the conditions in a burrow 
are widely different from those which prevail out- 
side is sufficiently shown by Pitman's observation 
on the Jerboa, Jaculus loftusi, in Lower Mesopotamia. 
This species is absolutely nocturnal. " Their earths 
go steeply into the ground for 2 or 3 feet and the 
Httle creatures evidently lie up all day in the cool, 
damp earth as I always noticed that captive speci- 
mens, of which we tried to keep many from time 
to time, suffered tremendously from the great heat 
during the day, even when kept in the coolest of 
places dug right into the ground, so much so that 
we never managed to keep any alive for more than 
a few days." 

Among the burrowing insects one must mention 
two groups, the Crickets and the Ants. Species 
of Cricket (GryUidse) are often found even in the 
more barren parts of the Great Palaearctic Desert ; 



104 ANIMAL LIFE IN DESERTS 

they take refuge by day in burrows dug under 
stones, and issue forth at night when the air is cool 
and the humidity not very low : the ants have 
successfully overcome the cHmatic difficulties, and a 
number of species may be found in the Great Palae- 
arctic Desert and in Central AustraUa ; many of 
them come up from their subterranean nests in 
the morning and late evening, but others are active 
during the heat of the day. 

In the group of animals which uses burrows 
constructed by other animals are included the 
majority of desert snakes and Uzards (at any rate 
in the Great Palaearctic Desert) and a number of 
nocturnal beetles (especially some Carabidae and 
such Tenebrionidse as Blaps). 

Many larger creatures, whose powers of movement 
enable them to rest at some distance from their 
feeding-grounds, take refuge in caves. Conditions 
in a cave differ fundamentally from those prevailing 
in the open desert : in the cave, temperature is 
nearly constant, humidity is more constant and 
higher than in the desert, and Hght is absent (C. B. 
WiUiams). But for the presence of caves the 
existence of bats in desert areas would be impos- 
sible, but in deserts in which caves occur, particu- 
larly if drinking-water is available, bats are fre- 
quently numerous, both as species and as individuals. 
Birds which nest or which roost in caves are quite 
an important element in the fauna of the Great 
Palaearctic Desert : examples are sub-species of 
the Eagle Owl {Bubo bubo) and Little Owl (Athene 
noctua), and of the Swifts (Gypselus apus, 0. murinus, 



ANIMALS— PHYSICAL ENVIRONMENT 105 

and C. affinis), and of the Rock Dove {Columba 
livia). 

None of these sub-species are very highly modified 
for hfe in the desert, and the species from which 
they are derived are distinguished for their abiUty 
to Hve in many types of cUmate and country ; 
in fact, the two owls, the dove, and the Common 
Swift all breed as far north as Northern Europe. 
It seems that the presence of caves, with their 
relatively unvarying temperature and humidity, 
may have enabled these vigorous and adaptable 
species to penetrate a short distance into the desert. 
Certain of them now breed and roost in houses 
and ruins, but this is clearly only a slight extension 
of the cave-haunting habit. 

It is probable that a closer study of the cave fauna 
in such countries as Egypt and South Palestine 
would reveal most interesting forms of Hfe. The 
contrast in cKmate between open desert and cave 
is so great that the colonization of the cave by 
animals which are specialized to hve in the sur- 
rounding desert would present great difficulties. 

The eggs of birds which breed upon the surface 
of the desert and are exposed to its summer climate 
are in a position of great danger, because if they 
are left uncovered by the parent birds they are 
rapidly killed by the heat during the daytime. 
It should be remembered that, at any rate in the 
Great Palsearctic Desert, most of the birds breed 
during the hot weather, e.g. Sandgrouse (page 85), 
Common Pratincole, and others. It is only the 
largest of eggs, those of the ostrich, which can 



106 ANIMAL LIFE IN DESERTS 

survive prolonged exposure to the desert sun. 
Though it is extremely difficult to disentangle truth 
from fiction in the case of the wild ostrich, I think 
that the following facts are now established. Neither 
in Africa nor in Arabia do ostriches bury their 
eggs in the sand, as is frequently stated. The 
eggs are often left entirely uncovered and exposed 
to the heat in the middle of the day, particularly 
in the hotter parts of the bird's range. At other 
times of the day, and particularly in the colder parts 
of the bird's range, the eggs of the ostrich are 
incubated by both parents in turn. 

Smaller eggs, which are more rapidly penetrated 
by heat, are quickly killed under conditions which 
merely serve to incubate the great eggs of the 
ostrich. The existence of this danger was clearly 
demonstrated during the fighting round Kut el 
Amara, and in other places in Mesopotamia, where 
many eggs of Sandgrouse were destroyed by the 
sun because the parent birds were driven from 
their eggs by gunfire. 

C. B. Ticehurst tells me that such eggs as those 
of Geochelidon nilotica, Glareola pratincola. Sterna 
caspia, and Larus gelastes are killed by exposure to 
hot sun. These birds are not desert breeders, but 
nest upon mud-banks under conditions which fre- 
quently approximate to true desert during the 
breeding season, and his observations are therefore 
pertinent. 

The devices to which the parent birds resort 
to avoid such fatalities are extremely interesting 
because they are so varied. Many desert breeders 



ANIMALS— PHYSICAL ENVIRONMENT 107 

place their nest as far as possible under shelter, 
most Larks under a small bush, all Wheatears in a 
hole or small cave, Hey's Partridge and See-See 
(Ammoperdix) in holes in small cliffs, or under 
boulders. Of the birds which breed in the open 
without protection from rocks or bushes, most 
species sit upon the nest from the time the first 
egg is laid. The eggs are therefore kept at a nearly 
constant temperature by the bird's body, and are 
not exposed to the heat by day and the cold by 
night. It appears to be established that Sand- 
grouse incubate from the time of laying the first 
egg, though Meade-Waldo's observations in an 
aviary in England do not support this view. 

It is recorded that the Pratincole (Glareola pra- 
tincola) stands over its first egg, and by doing so 
protects it from the sun's rays, and that a small 
Tern (Sterna saundersi) which breeds on the bare 
shore at Karachi (Sind) does the same. 

After incubation has commenced the majority 
of desert birds are unwilling to leave their eggs, 
and if they are compelled to do so they return 
to them as quickly as possible. This has been 
noticed by several observers of the Coiu-ser (Cur- 
sorius gallicus) and Sandgrouse. The eggs of the 
Sandgrouse have additional protection from heat, 
for when one parent returns from watering, and 
reheves the other from the duty of incubation, its 
breast is saturated with water. Therefore it appears 
that the eggs and the soil on which they are laid 
are wetted every day, which must tend to prevent 
overheating. 



108 ANIMAL LIFE IN DESERTS 

The Kitlitz Plover (Charadrius pecitarius), which 
breeds in tropical Africa and which extends down 
the Nile Valley to Lower Egypt, and its relative 
Charadrius alexandrinus seehohmi cover their eggs 
with sand when they leave them. The purpose of 
this is unknown : it may be protection from foes 
or from the sun's heat. 

iv. Animals and Wind 

We have already seen (pages 27-30) that wind 
is a constant element of the desert cUmate, at any 
rate in summer. It is frequently strong, and even 
violent ; in many places it is constant in direction, 
and under certain circumstances columnar vortices 
are formed which sweep small objects from the 
surface of the desert and carry them to a great 
height. It is probable therefore that wind is a 
great distributor of the seeds of desert plants, and 
of all the smaller forms of animal life. The great 
majority of the creatures which it carries before it 
or sweeps up into the sky are doubtless killed by its 
violence, but of those which survive a smaU number 
reach a suitable environment far from their original 
home. 

It seems probable therefore that wind has had 
a large share in widening the distribution of many 
of the plants and animals of the Great Palsearctic 
Desert, and it is important to remember that the 
desert wind is barely if at all impeded by herbage 
and grass, as it is in other types of country. It is 
therefore felt in its full force even by the small 
forms of life on the surface of the ground. 



ANIMALS— PHYSICAL ENVIRONMENT 109 

The effect of the wind upon the flora Indirectly 
affects the fauna. To the plants it is harmful 
both by reason of the physical damage done by 
violent gusts and wind-blown sand and small 
pebbles, and also because it rapidly dissipates the 
sHghtly moist air which accumulates round the 
plant owing to transpiration. Increased transpira- 
tion results, that is to say, increased loss of water 
which is already very scarce : it foUows that plants 
may be able to exist on a specified amount of water 
if they are protected from wind, and may be killed 
if they are exposed to the wind. 

This is well seen wherever a wind of constant 
direction blows through a narrow valley ; any 
large rock which breaks the force of the wind, 
and thereby reduces evaporation and transpiration 
under its lee, shelters a richer flora than wiU be 
found elsewhere. 

It is in fact true that places exist which are desert 
primarily because of wind. For instance, through- 
out great parts of the Libyan Desert the distribu- 
tion of plants is determined rather by the presence 
of shelter from wind than by any other influence. 

The effect of a strong wind loaded with sand upon 
the very scanty spring vegetation on the Libyan 
border of Lower Egypt is thus described by Thomas. 
"On April 13, towards the close of the growing 
period of most plants, a hot wind blew in from the 
desert for about five hours, raising great clouds of 
sand which drove along the surface of the groimd 
like mist. The temperature went up considerably, 
in spite of the sun being obscured, and was over 



110 ANIMAL LIFE IN DESERTS 

45° C. : the air felt intensely dry and was charged 
with sand-grains which produced a smarting effect 
on the exposed skin. The wind went down during 
the night, but it remained hot and no dew fell. 
The storm continued in this way for the next two 
days, and its effect on the vegetation was very 
striking. All flowers and young parts of plants 
had shrivelled, the upper portions of the green 
branches of Calligonium had died and had often 
been broken off, the fruits of this plant had dried 
and had become quite hard : most of them were 
detached from the plants and were blown about 
in all directions. The upper portions of the stems 
of Heliotropium luteum were withered and dead, 
and had lost all the younger leaves. AU the plants 
appeared very much withered, except Imperata 
cylindrica, which seemed untouched. Many plants 
seemed partially uprooted, especially PuUcaria and 
Polygonum ; in reahty the wind had removed the 
surface layers of the sand round them, and 20-25 cm. 
of rootstock were exposed — this showed the im- 
portance of being deep-rooted. The surface roots 
of Panicum turgidum were very frequently laid bare. 
In other cases plants were wholly or partially bm^ied." 
The direct effect of wind upon the animals, 
especially the smaller animals, also merits discussion, 
as it has apparently caused modification of habit in 
some animals and of structure in others. Certain 
small Blue Butterflies (Lycaenidae) which inhabit 
the Great Palsearctic Desert possess the power of 
continued flight within one small bush, from the 
shelter of which they seldom issue. Butterflies of 



ANIMALS— PHYSICAL ENVIRONMENT 111 

the genus Tarucus may be observed flitting up and 
down continuously inside a bush of Zizyphus, with- 
out leaving the middle of the bush, and sometimes 
continuing in flight for many minutes. The minute 
Chilades galba, another member of the same family, 
is able to limit its flight within a plant of Ononis 
(" Rest Harrow "), which is only a foot in circum- 
ference, and to remain on the wing in this Uttle bush, 
when such a wind is raging outside as to prevent 
the flight of all other butterflies. 

Another interesting modification of habit has been 
observed by Hartert, Rothschild, and others in the 
Algerian Sahara. The prevalent wind is from the 
east, so that the sand and debris which it carries 
settle on the west side of any bush or stone, because re- 
lative calm prevails under the lea of the bush. Several 
species of Passerine birds regularly make their nest 
against the windward side of small bushes, and so 
avoid being smothered with sand and debris. They 
then fortify the outer side of the nest with a mass of 
pebbles, apparently in order to protect the nest 
from wind. This seems to be the invariable habit 
of Clot-bey's Lark {Rhamphocorys clot-bey), which 
collects pebbles weighing as much as half an ounce. 
In the Larks Ammomanes phoenicurus arenicohr and 
Eremophila alpestris hilopha, the habit of placing 
the nest on the windward side of a smaU bush is 
apparently universal, but the barricade of stones is 
occasionally very small or quite absent. The nests 
of the Trumpeter Bullfinch {Erythrospiza githaginea 
zedlitzi) are invariably on the windward side of small 
bushes, and perhaps protected by their position 



112 ANIMAL LIFE IN DESERTS 

immediately under the bush, for they were without 
a barricade of stones. One species of Wheatear 
(Saxicola leucura) has a similar habit, nesting under a 
rock and almost blocking the passage to the nest 
with a mound of pebbles : the bird does this in the 
Algerian Sahara, and also in the Sudan. Another 
Wheatear {8, leucopyga cegra) shows what is probably 
a development of the same habit, for it nests in holes 
in rocks and crevices in walls and constructs a wide 
path of flat stones up to the mouth of the crevice. 

Similar habits have been observed in other 
countries, but no information is given as to the 
direction of the prevalent wind, or the side of the 
bush under which nests were habitually built. In 
the Sudan Chapman has recorded the building of 
barricades by an Ant-Chat (Oercomela scotocerca) 
and a Lark {Ammomanes deserti), and states that 
the Cercomela collects as many as 130 pebbles in 
its barricade. This habit is the more remarkable 
as it has been developed by birds which are not 
closely related to one another ; one presumes that 
it has originated independently in the Finch, in the 
Wheatears and Ant-Chat which are closely related, 
and at least once among the Larks. 

Of modifications of structure which are apparently 
induced by the wind, the most striking is the 
winglessness of many insects whose near relatives 
in other types of country are winged. In the order 
Orthoptera one may observe several series of insects 
in which the wings are progressively reduced. Some 
species have the wings so shortened that they are 
useless for flight, but normal in structure and 



ANIMALS— PHYSICAL ENVIRONMENT 113 

proportions ; in others they are present as minute 
vestiges, or so reduced that their sole function is to 
assist in the production of the insect's chirrup. 
In some species the reduction has proceeded much 
further in one sex than in the other. Short-winged 
forms may be observed in the Long-horned and 
Short-horned Grasshoppers, in the Mantis family, 
and in the Crickets, so that they must have arisen 
independently many times in the Orthoptera. The 
phenomenon is not by any means confined to desert 
species, but is much more frequently seen in them 
than in those of other environments. For instance, 
in Algeria and Tunisia about half the Orthoptera 
are wingless, even when the forms which inhabit the 
fertile coastal region are included in the count. 

Among the Coleoptera (Beetles) fusion of the 
wing-cases and consequent flightlessness is a char- 
acter of very many Tenebrionidse (Fig. 42, facing p. 
150) and Carabidae (Ground Beetles) in deserts. Loss 
of the power of flight in these two families of beetles 
and in the Orthoptera is not confined to species 
which inhabit deserts, but is much more common 
among them than among others. That it is due 
solely to the wind and not to any other infiuence is 
apparent from the fact that a similar loss of the power 
of flight occurs in many other environments which 
are exposed to violent winds, but do not in any 
other respect resemble deserts : the insects of 
mountain tops and of small isolated islands furnish 
examples. 

The dispersive effect of the wind upon small 
animals can be exercised in the absence of any modi- 



114 ANIMAL LIFE IN DESERTS 

fications either of structure or of habit. This is seen 
in the case of caterpillars of the famiUes Arctiidae, 
Lymantriidae (Liparidae), and Lasiocampidae. These 
hairy caterpillars are abundant in the semi-deserts 
of Algeria, Southern Palestine, and other countries 
in the spring-time. In places where the annual 
vegetation is not too dense one may see them roUed 
up and blown along the ground for many yards by 
a gust of wind. They are not more hairy than their 
congeners in Europe, so that in this case we have a 
number of insects which are able to benefit by the 
desert winds without modifying either their habits 
or their structure. 

Of the destructive effect of desert wind upon small 
creatures, especially small winged creatures, very 
little is known. It is on record that small birds 
have been dashed against a waU and killed in the 
Hebrides, and there is every reason to suppose 
that the violent winds which occasionally visit some 
deserts are equally destructive. The destruction of 
swarms of locusts by wind which blows them into 
the sea has been famihar since the dawn of history. 

V. Relationships with Soil 

There is no doubt that each type of desert soil 
presents its special problems to the fauna and flora 
and is inhabited partly by generaHzed forms which 
are able to exist in many types of desert or even 
outside the desert, and partly by specialists which 
are limited to clay or rock or sand, or other special 
soil. Information on these points is at present very 
meagre and fragmentary, except with regard to the 



ANIMALS— PHYSICAL ENVIRONMENT 115 

fauna of sandy desert. To that, therefore, I propose 
to confine our attention entirely. 

It has been shown (page 40) that sand probably 
presents more difficulties to the desert flora and 
fauna which attempt to colonize it than does any 
other type of desert. It is not, therefore, to be 
wondered at that the fauna of sandy areas, and 
particularly of areas in which the sand is loose, is a 
small one, and that it consists largely of animals 
which in overcoming the difficulties of life in sand 
have become unfitted for life in any other environ- 
ment. 

Grinnell has described the conditions of life 
of certain species of sand-living rodents in the 
North American deserts. The Round-tailed Ground 
Squirrel (Citellus t, tereticaudus) requires large areas 
of sand, and also bushes, under which it can burrow : 
it is frequently abroad in the daytime, but it avoids 
direct sunshine by passing rapidly from the shade 
of one bush to that of another. It cannot endure 
the fierce heat of midday on bare sand, and if an 
individual is caught in a trap uninjured but exposed 
to the sun's rays it dies quickly. This rodent is 
therefore an animal which requires the co-existence 
of a geological and floristic factor, in order to enable 
it to live in a particular place. The Big Desert 
Kangaroo Rat {Dipodomys deserti, Fig. 38) lives in 
the same sandy places as the Round-tailed Ground 
Squirrel, but its requirements are quite different. 
It is nocturnal, and is sheltered in its burrow from 
the conditions which prevail during the day; it 
is therefore indifferent to the presence of bushes. 



116 ANIMAL LIFE IN DESERTS 

What it requires is blown sand which must be at 
least a foot deep. The probable explanation is that 
sand is the only soil in which it is able to burrow ; 
for its incisors are weak, and its claws and feet smaU. 
In fact, what determines the presence of this rodent 
in a given spot is the coexistence of two physical 
factors, loose sand for its burrows, and sufficient 
depth of sand to accommodate it. 

Associated with the Big Desert Kangaroo Rat, 
and largely dependent on it for food, one finds the 
Kit Fox ( Vulpes macrotus arsipus), which is a purely 
desert animal and apparently occupies the same 
place in nature in the American sandy deserts as the 
Fennec Fox in Africa. The Fennec Fox {Vulpes 
zerda) Uves exclusively in sandy places in the Sahara 
and Egypt ; it is a small, rather weak fox, which 
feeds upon beetles, grasshoppers, vegetable matter, 
and a few small rodents. 

The Marsupial Mole (Notoryctes) of Central Aus- 
traUa is an inhabitant of sandy places. It possesses 
the general outward form of our own Mole (Talpa), 
and of other burrowing mammals, to none of which 
is it in any way related. It is a cyUndrical animal, 
with strong shovel-shaped feet, and a reduced tail, 
and it has no eyes. It makes no definite runs, 
because the sand collapses at once after its passage, 
but it spends its time pushing through the sand in 
search of insects, particularly ants. The Tuco-tuco 
(Ctenomys), a rodent of South America, exhibits 
many of the external characters of the mole, though 
it is related neither to the mole nor to Notoryctes. 
It is found in isolated colonies wherever sandy 



ANIMALS— PHYSICAL ENVIRONMENT 117 

patches occur in the pampas and semi-deserts of 
South America, and there is a tendency for the 
individuals of each colony to differ in colour, size, 
and other characters from those of other colonies. 

The reptiles found in sand are pecuUarly interesting 
because they show many examples of convergence. 
Camp, in describing the habits of the reptiles of 
South-Eastern California, states that in one burrowing 
snake and three lizards the rostrum is specially 
developed, protruding beyond the mouth. These 
lizards belong to several different families, so that 
this similarity in the rostrum is due to convergence 
and not to close relationship. 

The same enlargement of the rostrum has been 
recorded by other authors in several different genera 
of snakes which burrow in the light soil or sand of 
arid regions : rather similar are the fringed scales 
surrounding the eye in some sand-dwelling Uzards. 
In the Jerboa (Jaculus) the muzzle can be contracted 
and the nostrils narrowed and almost covered by a 
fold of skin. It appears that the function of this 
is to protect the nostrils when the animal is burrow- 
ing and pushing soil with its broad snout (Anderson 
and De Winton, and Pocock). 

Certain lizards and snakes possess the power of 
burrowing into sand with extraordinary rapidity. 
The lizards which do so do not use their legs, but 
progress by rapidly bending the body from side to 
side. In members of the Skink family (Scincidse) in 
North African deserts this is associated with pro- 
gressive reduction of the Hmbs, and members of this 
family exist showing various stages from the normal 



118 ANIMAL LIFE IN DESERTS 

complement of four legs to complete absence of 
Mmbs. 

Many lizards living in sandy places are extremely 
rapid in their movements. When they are not 
running they stand alert with the head held high 
and the front part of the body raised on the fore-legs, 
and when they are in motion the tail is held weU 
above the ground as a counter-balance. This holds 
good of lizards of several families, from several parts 
of the world ; and the species which are predaceous 
and those which are preyed upon both exhibit it. 
In many of them the toes of the fore- and hind-feet 
are broadened by a fringe of elongate scales. Appar- 
ently aU of these species Hve on sand, some of them 
on great stretches of dune, others on the small heaps 
of blown sand which accumulate under bushes in 
deserts of mixed stone and earth : it seems legitimate 
to conclude that the fringe widens the surface, which 
presses on loose sand and acts in the same way that 
a snow-shoe does on loose snow. As Figs. 39 and 40 
show, these fringes are developed in several families 
of lizards, in deserts in different parts of the world. 
Of the seven genera figured Phrynocephalus (A) is 
an Agamid from Transcaspia ; Acanthodactylus (B) 
and Scaptira (C) are Lacertidse, distributed in the 
Great Palsearctic Desert ; CaUisaurus (D) is an 
American Iguanid ; Teratoscincus (E), Stenodactylus 
(F), and Ceramodactylus (G) are Palsearctic desert- 
Hving Geckonidse. It is clear that this curious 
character has been developed on at least half a 
dozen different occasions, and it is clear also that it 
is a response to Ufe on sand. I am most grateful 



ANIMALS— PHYSICAL ENVIRONMENT 119 

to Miss J. Procter, of the British Museum (Natural 
History), for her kindness in selecting these most 
interesting Hzards. 
Among the insects, the ants which hve in sandy 





B 





'm=^ 




Fig. 39. — Fore -FEET op the following Lizards : — A. Phrynocephalus 
mystaceus ( x 1^^). B. Acanthodactylus scutellatus ( X 2). C. Scap- 
tira grammica (x 2). D. CalUsaurus (Uma) scoparius. After Cope, 
" Amer. Nat.," 1894. E. Teratoscincus scincus ( X 2). F. Stenodactylus 
guttatus ( X 3). G. Ceramodactylus dorice ( x 3). 



and dusty places are remarkable. In very many 
of them a " circum-oral crate " of stiff bristles is 
developed upon the structures which surround the 
mouth. The purpose of this is clearly not connected 



120 



ANIMAL LIFE IN DESERTS 



with feeding, for it is well developed in harvesting 
species, in predators, and in honey-pot ants (page 72). 






Fig. 40. — ^Hind-feet of the following Lizards : — A. Phrynocephalus 
mystaceus ( x 1^). B. Acanthodactylus scutellatus ( X 2). C. Scap- 
lira grammica (x 2). D. CaUisaurus (Uma) scoparius. After Cope, 
" Amer. Nat.," 1894. E. Teratoscincus scincua ( X 2). F. Stenodactylus 
guttatus { x 3). G. Ceramodactylus dorice ( x 3). 



Wheeler suggests that it is used to clean the strigil 
on the fore-leg, which in turn is used for cleaning 



ANIMALS— PHYSICAL ENVIRONMENT 121 

the antennae, etc., and that it is only developed in 
ants from sandy and dusty places because the 
strigil is peculiarly likely to become clogged in such 
places. 

The protozoa of the sand in the neighbourhood 
of Cairo have been investigated by Thomson and 
Thomson. These microscopic animals exist in the 
dry sand in a resistant envelope or " cyst," from 
which they only emerge when the sand is moist, 
and as it dries they again envelop themselves in 
" cysts." In the climate of Cairo their period of 
activity is reduced to a few days a year, and their 
period of dormancy is extremely protracted. They 
are exposed to light and heat and drought in the 
sand, and yet the investigators were able to recover 
about fifty species from the sand after eight months 
of drought. Most of them belonged to forms known 
elsewhere from fresh water ; that they were depend- 
ent on occasional moistening is shown by their great 
rarity in the sand of Luxor in Upper Egypt, in an 
area which is without rain in the average year. 



CHAPTER VI 

RELATIONS BETWEEN ANIMALS AND 
PLANTS 

Interrelationships between animals and plants 
may be divided into that class in which the animal 
is dependent on the plant, and that in which the 
plant depends upon the animal. The first group 
of relationships is the larger, in deserts as in other 
types of environment. AU the world over it is 
true that the animal depends on the plant for 
compounds of nitrogen and compounds of carbon : 
most of the essential food of every Uving animal 
comes directly or indirectly from plants, and with 
it the animal swallows a proportion of water. The 
plants also fulfil certain subsidiary functions with 
regard to the animals; they furnish them with 
shelter from the elements, and protection from 
enemies. One may therefore say in general terms 
that the plant provides the animal with food and 
water, and with shelter and protection. 

It is convenient to consider at one time the food 
and the water which animals in deserts derive 
from the plants which they eat. The food and 
water are swallowed together, and may for the 
moment be regarded as a single contribution made 

122 



V 

1.^ 



RELATIONS OP ANIMALS AND PLANTS 123 

by the plant kingdom to the animals. It must be 
remembered that in the desert this source of water 
is of much greater importance than it is imder 
other conditions. In most environments the water 
which is part of the food material is incidental : 
in the desert it is essential, and commonly the only 
available supply. 

We have already (Chapter III) divided the 
desert flora into three biological groups — the annuals, 
the perennials which he buried during the un- 
favourable season, and the perennials which exist 
above the surface of the ground at all seasons. 
Let us see how each of these groups is used by the 
animals as a source of food and water. 

The conditions which are best for the annuals, 
and which lead to the production of abundant annual 
vegetation after rain has fallen, are favourable also 
to many animals. No sooner have the young annual 
lants appeared above the earth than they are 
attacked by numbers of caterpillars, bugs, leaf -eating 
beetles, wood-Hce, and other plant-eaters : as soon as 
the blossoms open they are visited by bees, butterflies, 
moths, thrips, flower-eating beetles, and many other 
small creatures in search of nectar or pollen or 
petals. For a very short time the cUmate and the 
floral environment is favourable to insects in 
general. Then the soil dries, the air becomes hot, 
and most of the flowers and insects disappear. 

The majority of insects which are dependent on 
the annual vegetation in the Great Palaearctic 
Desert are active for a very short period and exist 
through the dry nine months of the year in a state 



124 ANIMAL LIFE IN DESERTS 

of dormancy, some of them as pupse, others as eggs, 
others probably as resting larvae. A few species 
prolong their season of activity and produce a 
series of broods by utiUzing first one food plant and 
then another, as the plants successively become 
available. A good example is furnished by Papilio 
machaon, the Swallow Tail Butterfly, in Mesopo- 
tamia. In April and May it fed on the flowers of 
Ruta tuherculata, and as this plant began to go to seed 
Ammi ma jus came into flower, and became for the 
moment the plant on which eggs were most com- 
monly laid. This plant was followed by Ducrosia 
anethifoUa, which was not common, and probably 
not an important food plant. While A, ma jus and 
D, anethifolia were running to seed, Ammi visnaga 
flowered and became an important food plant ; it 
was in full flower in June after the first three were 
quite dry. A fifth plant, Foeniculum vulgare, was 
also found to be eaten by the larvae of P. mxichaon. 
It seems then in Mesopotamia that the Swallow 
Tail Butterfly has a regular succession of food 
plants belonging to two unrelated natural orders 
of plants — the Ruta to the Rue family, the others 
to the Umbelliferae (Peile). One might argue from 
this that if a caterpillar or other plant-eater pos- 
sesses the power of living on a variety of plants it 
may be able to survive under conditions which 
would exterminate another caterpillar that could 
only feed on one plant : in fact, that polyphagy 
may be one factor determining the survival of 
certain species in the desert. 

In rather a similar way I noticed in Mesopotamia 



RELATIONS OF ANIMALS AND PLANTS 125 

I that a very large number of species of bees, fos- 
sorial wasps, ruby wasps, and true wasps congre- 
gated at whatever plant was in bloom. The 

pHymenoptera could not afford to indulge their 
preferences ; every species which was on the wing 
might be taken now in a field of beans in flower, 
a few weeks later at Zizyphus blossom, or Acacia 
(Prosopis), or Lycium ; many of the species remained 
on the wing during long periods, and a particular 
species might frequent half a dozen different flowers, 
each one exclusively for a short season. Such a 
thing does not, I think, happen in lands where 
flowers are commoner and the flowering season is 
more prolonged. 

The inroads upon the annual vegetation of the 
larger grass-eating mammals, for instance, the 
gazelles and hares in the Old World, are relatively 
unimportant because the numbers of these animals 
are limited by the scarcity of fodder during the 
dry season. Spencer showed that adults of the 
marsupial Phascogale cristicauda in Central Australia 
were 40 per cent, to 60 per cent larger at the close 
of a good season following rain and plenty of vege- 
tation, than they were in a season in which rain 
had been deficient. He beheves that this explains 
the great variation in size which may be observed 
among adults of other species of small marsupials. 
It is only such small beings as the insects, with their 
power of lying dormant in unfavourable seasons 
and of rapid multiplication, which can take advan- 
tage of the annual flora of the desert. 

The plants of the second biological group, those 



126 ANIMAL LIFE IN DESERTS 

which store food in bulbs, tubers, and other struc- 
tures underground, and are only above ground for 
a short season, are probably of considerable impor- 
tance to the fauna, but we have Httle actual know- 
ledge on this point. Tristram, in speaking of the 
deserts of Southern Palestine, says : " The vast 
number of little rodents in apparent deserts is 
explained by the nature of their food, which is 
chiefly supplied by bulbous roots. The greater 
part of the desert plants are tuberous or bulbous, 
and after nine months of utter barrenness, the first 
winter rains soon carpet the waste with a brilliant 
spangling of bulbous flowers — crocus, iris, squiUs, 
asphodels, cyclamen, and others. Their glory is 
soon over ; but the large succulent roots remain, 
retaining their moisture through the summer, and 
affording abundant nutriment to the Httle bur- 
rowers." Hart states that the wild boar wanders 
far out into the semi-deserts of Beersheba in order 
to root for bulbs, particularly those of the great 
squill (Urginea, Fig. 26), and that in consequence 
roots of this plant become quite difficult to obtain. 
In the burrow of a Mole-rat (Spalax), in Egypt, 
Anderson found a store of sixty-eight bulbs, but he 
does not state the species of plant to which they 
belonged. 

It is natural that animals should be particularly 
associated with plants of the third group, which 
are above ground at aU seasons of the year, and 
which supply food and water even at unfavourable 
seasons to the creatures which can make use of them. 
Many examples might be found of mammals and 



RELATIONS OF ANIMALS AND PLANTS 127 

birds which subsist largely or entirely on some 
particular desert perennial. In Mesopotamia we 
observed a very close relationship between the salt- 
loving bush (Suseda) and a Dwarf Gerbille {Dipo- 
dillus dasyurus). The Suaeda was a bush about 
3 feet high and grew in salt patches in the desert : 
a few bushes of Atriplex and Salsola were the only 
plants found associated with it, and they were not 
common. Several insects lived on the Suseda, and 
the Dwarf Gerbilles Uved on any insects they could 
catch, and on the succulent leaves of the plant. 
They required no water in captivity, and in nature 
they and the Suaeda bush lived far from the River 
Tigris : there is little doubt that they were entirely 
dependent on it, and the insects found upon it, for 
food and water. The desert was flat and composed 
of silt : it was devoid of any form of shelter except 
the Suseda bushes, and among its roots the Dwarf 
Gerbilles made their burrows. We may therefore 
suppose that they derived from the plant not only food 
and water but also protection from the foxes and 
occasional jackals which existed in those parts of 
the desert. So far as I know only one other 
mammal, a hare {Lepus connori), occurred in the 
salt patches of desert where the Suseda flourished. 
It is natural that the animals should be few in a 
place where only one plant grows and no water 
can be obtained except from the plant, and it is 
noticeable that three of the four mammals, the 
fox, jackal, and hare, are active cursorial forms able 
to wander far from the Suseda patch in search of 
water and food. 



128 ANIMAL LIFE IN DESERTS 

In the same way it is stated that Pallas' Sand- 
grouse {Syrrhaptes paradoxus) feeds very largely on 
a salt-loving desert Chenopodiaceous plant, Agrio- 
phyllum, in Central Asia. 

Such close connection between the animal or 
bird and the plant on which it lives is obviously 
a potential danger to it. A severe drought, a fire, 
a flood, or some other natural cataclysm, such as 
is not uncommon in deserts, may exterminate bird 
and plant together, at any rate over a part of their 
range. 

The plants which are most important as fodder 
for domestic animals in deserts belong to those 
perennials which live above ground at all seasons. 
Sheep in the more arid parts of AustraUa depend 
largely upon salt-loving succulents (Zygophyllaceae 
and Salsolacese), particularly during periods of 
drought, and in the drier parts of the southern 
United States plants of the Cactus family are used 
in the same manner. 

I can recall only one instance of animals depen- 
dent upon plants for water and not for food, and 
that was observed in the hill country of Palestine, 
which is certainly not desert, and barely falls within 
our definition of semi-desert. However, in the 
rainless summer, the season at which this obser- 
vation was made, the country is extremely arid, 
and the observation is, I think, suggestive enough 
to warrant inclusion here. AH over the hills of 
Judaea and Samaria there grows a genus of stout 
thistles (Echinops) with spiny globular heads. These 
flower in June and July when water is very scarce. 



RELATIONS OF ANIMALS AND PLANTS 129 

A large weevil {Larinus maculatus) and a Rose 
Chafer {Protcetia libani) bite into the flower-heads 
of this thistle, and feed on the interior, leaving an 
open wound from which the sap continues to run. 
This sap is drunk greedily by smaU bees, and wasps, 
and ants, and would not be available to them 
imless the weevil or chafer had first bitten into 
the thistle. Such a method of obtaining drink is 
not, of course, peculiar to desert cUmates ; the sap 
which exudes from tree-trunks injiu*ed by Goat 
Moth or other wood-borers, in Great Britain, attracts 
butterflies, beetles, flies, and other insects. 

Cases in which the animal depends on a plant 
for food and water might be multiphed. The 
relationship between Dwarf Gerbille and Suaeda, in 
which protection as well as food and water is in- 
volved, leads us on to another group of associations, 
in which the principal or only bond between plant 
and animal is shelter from climate or protection 
from enemies. 

Such an association was studied by Hartert in 
the northern Sahara, a short distance south of 
Biskra, in Algeria. He describes it thus : " After 
leaving Bordj Saada the tamarisk bushes disappear 
and a wide sandy plain covered with innumerable 
stones extends to far beyond Bordj Chegga, where 
the sand begins to prevail more and more. The 
sandy plain, however, is not smooth or even, but 
covered with countless little sandhills, the nucleus 
of which is, or has been in each case, a bush of 
Limoniastrum, Salsola, or other plant. Each iso- 
lated plant arrests the sand that flies across the 

K 



130 ANIMAL LIFE IN DESERTS 

plain with every wind, and winds are frequent, 
and a miniature dune is formed ; the plant is partly 
protected by the surrounding sand, but the latter 
runs down from the top and threatens to suffocate 
the plant, so that it strives for air and grows up- 
wards, dying off at the lower end. Thus the hiUock 
grows and grows and is crowned with a plant, imtil 
the latter dies off and a little mountain remains. 
These sandhills, hardened more and more in the 
course of time, form the centres of all the animal 
life except some of the birds. In these hillocks a 
rodent, Meriones getulus, the Djerd of the Arabs, 
makes its holes, which are used for nesting by 
CEnanthe (Saxicola) moesta, and are sometimes in- 
habited by the dreaded, deadly Asp {Cerastes 
cornutus), the Lefa of the Arabs, and a beautiful, 
harmless snake, Zamenis diadema. In these hillocks 
one sees disappearing the pretty Hzard, Acantho- 
dactylus scutellatus, and in them hides the nocturnal 
Gecko, Stenodactylus guttatus. Also the beetles, 
the common Anthia sexmaculata and Graphipterus, 
and the rare and gigantic Anthia venator, as well as 
some Tenebrionidse, disappear among these hillocks, 
the former with wonderful swiftness. In this sandy 
plain also, stony patches occur, Kke little islands 
in the sea of sand, and on these is found the pale 
Crested Lark (Galerida theUce deichleri). Along the 
roads and on the sand we see another species of 
Crested Lark {G. cristata arenicola), which it is 
almost impossible to miss, while the first form is 
easily overlooked when one does not know exactly 
where to search for it; this was the reason why 



RELATIONS OF ANIMALS AND PLANTS 131 

we only discovered its real home on our way back." 
Here the bond between the animal and the plant 
is mainly that the animal obtains shelter from the 
plant, or from the sand accumulated by the plant ; 
but we know from other sources that the " Djerd," 
as well as other Gerbilles, are largely dependent 
on the Limoniastrum leaves for food and water. 

A most interesting case of the same nature, but 
one in which the animals obtain shelter, but not 
food or drink, from the plant, has been studied in 
Arizona and California, by GrinneU and other 
American naturahsts. The Saguaro, or Giant Cac- 
tus {Cereus giganteus\ is a picturesque and very 
interesting inhabitant of those deserts (Fig. 41). 
It is an upright cylindrical plant, with very few 
branches, and covered with spines ; it attains a 
height of 30 or 35 feet, and a diameter of 2 feet 
6 inches. Its fruit is attractive to many species 
of birds, and according to Tuomey " nearly half a 
hundred birds feed upon the fruit of the Giant 
Cactus, the Hst including all our thrashers, wood- 
peckers, finches, and pigeons." But the Giant 
Cactus is not interesting only because birds eat its 
fruit, and as it harbours few insects one might sup- 
pose that there would be no close link between it 
and the birds for the great part of the year. A 
connection however exists, and it is a very close 
one. To quote from Grinnell : " It is clearly 
apparent that the critical feature of the saguaro 
which prescribes its avian dependants is nothing 
less than the favourable opportunity offered for 
the excavation of safe retreats in its trunk : and 



132 ANIMAL LIFE IN DESERTS 

only the two woodpeckers are equipped for making 
these excavations. So that, without the wood- 
peckers to make holes, the other birds would be 
no better off for the presence of saguaro." The 
two woodpeckers to which he refers are the Gila 
Woodpecker (Genturus uropygialis) and Mearn's 
Gilded Fhcker {Colaptes chrysoides mearnsi). The 
range of these woodpeckers is wider than that of 
the Giant Cactus, and they have been found breeding 
in trees of various species along the banks of the 
California River. But wherever the Giant Cactus 
grows the two woodpeckers are found, and found 
more commonly than in other places, and when 
it is possible the woodpeckers hew their nesting- 
hole in this plant and nothing else. But for its 
existence the birds would be confined to the river- 
side growth of Cottonwood and willow; but as 
they can excavate nesting-sites in the cactus they 
are able to colonize desert areas where no other 
large vegetation grows. Other parts of the same 
deserts where there is no Giant Cactus have a 
much poorer avifauna, for neither the woodpeckers 
nor the birds which are dependent upon them are 
foxmd there. The association between the Giant 
Cactus and the two woodpeckers is closer because 
the woodpeckers are strictly resident birds, remain- 
ing all the year where they breed, and not wandering 
far from that place at any season. As Grinnell 
impUes in the passage which I have quoted, other 
birds use the woodpeckers' nesting-holes, after the 
woodpeckers have vacated them. The Elf Owl 
(Micropallas whitneyi) is found exclusively in deserts 



RELATIONS OF ANIMALS AND PLANTS 133 

in which the Giant Cactus grows, and takes a dis- 
used woodpecker hole for its nesting-place. It is 
therefore dependent for its very existence on the 
presence of a particular cactus, and either of two 
particular woodpeckers. Less strictly dependent 
upon the cactus and woodpeckers are a Screech 
Owl (Otus asio gilmani), a Sparrow Hawk {Falco 
s'parverius), a Flycatcher (Myiarchus c, cinerascens), 
and other birds. None of these are confined to 
the area inhabited by the Giant Cactus, but they 
all inhabit that area, and within it they aU use old 
woodpecker holes as nesting-sites. 

Frequently a single trunk of the Giant Cactus 
contains nests of one or other woodpecker, and also 
of one of the birds which use the old woodpecker 
holes. Honey-bees also use these excavations as 
hives. One must remember that the number of 
Hving creatures which eventually depend upon the 
Giant Cactus includes the scavengers in the birds' 
nests and bees' nests, the insects, few though they 
may be, which devour it or frequent its blossoms, 
and many others. AU these organisms depend upon 
the growth of Cereus giganteus for their existence in 
certain areas. 

There are instances in which, contrary to the 
general rule, the plants are dependent upon the 
animals, and although these cases are not very com- 
mon in deserts, a few may be mentioned. Botanists 
teU us that there are two important agents, the 
wind and the insects, by which the pollen of plants 
is carried to the female flower, or female part of the 
flower, which it is intended to fertiUze. In many 



134 ANIMAL LIFE IN DESERTS 

environments the insects fertilize more plants than 
the wind does ; in deserts, perhaps because winds are 
so common and blow without impediment among the 
sparse vegetation, fertilization by wind is much 
commoner than fertiUzation by insects : but the 
insects, especially the bees, flower-eating beetles, 
butterflies, and thrips, which are often so numerous 
among the annual vegetation, no doubt fertiUze 
certain species of plant, though at present we have 
no clear knowledge on this point. One remarkable 
fact is known : Loranthus acacice, a plant related to 
the mistletoe, grows around the Dead Sea and in 
the Lower Jordan Valley, as a parasite upon various 
trees : it is almost certainly fertihzed by the Sun- 
bird (Cinnyris osm\ which probes the tubular 
blossoms with its long, curved beak. 

According to Kobelt the Marmot {Arctomys bohac) 
of Mongolia materially alters the character of the 
vegetation round its colonies. The soil which is 
thrown up round the burrows is suitable to special 
plant types which are not common, and do not occur 
together elsewhere in the steppe : round the colonies 
of this rodent, and in no other place, these peculiar 
" marmot gardens " are found. Bateson states that 
in the very uniform steppes of Central Asia man and 
his animals are a disturbing factor. Old camp-sites 
can be seen from a great distance, because of the 
patches of nettles which grow on them and not in 
other parts of the desert. 

The dispersion of seeds by birds and animals is 
common to all parts of the world. Seeds which are 
particularly suited to this means of conveyance are 



RELATIONS OF ANIMALS AND PLANTS 135 

generally provided with hooks with which they 
entangle themselves in the feathers or hair of passing 
creatures ; others are produced in a fleshy pulp, 
which is eaten, and some at any rate of the seeds 
pass unharmed through the intestines of bird or 
mammal, or stick to its exterior until they are 
deposited perhaps at a distance from the parent 
plant. Numberless examples of seeds and seed- 
vessels armed with hooks and spines could be quoted 
from the flora of the Great Palaearctic Desert, especi- 
ally from the annuals ; it is a common thing to 
find such " burrs " in large numbers in the coats 
of sheep, jackals, and even such smooth-haired 
animals as gazelles and jerboas. Fleshy fruits are 
not common in deserts, and many of those which 
occur are so bitter or nauseating, or in other ways 
unattractive, that they are shunned by the fauna. 
Schimper states that jackals disperse the seeds of 
CitruUus, presumably after biting the fruit, but I do 
not think this is a common occurrence. The fruits 
of many members of the Cactus family are sweet 
and fleshy, though protected by spines. I have 
already quoted Tuomey's remarks about the fruit 
of Cereus giganteus and the birds which are attracted 
to it ; Spalding adds that squirrels fatten on the 
fruit of Echinocactus ; one is probably justified in 
concluding that the seeds of the Cactus family are 
largely spread by animals and birds. The date- 
palm {Phoenix dactylifera) is entitled to a place on 
the Hst, though palms which produce fruit edible to 
man do not exist wild. 

Dates in Mesopotamia are eaten greedily by 



136 ANIMAL LIFE IN DESERTS 

several birds, but by none more than by Hypocolius 
ampelinus. These instances must not be supposed 
to imply that fleshy fruits are common in deserts ; 
the reverse is the case. 

Animals serve the plants by distributing their 
seeds, but they do immense harm to the vegetation by 
devouring plant and seed ahke. The deserts of the Old 
World support large numbers of domestic goats, sheep, 
cattle, and camels, and of wild gazelles, antelopes, 
and hares, and these animals Hve by browsing shrubs 
and herbs. In the neighbourhood of a bedawin 
encampment or an Arab village or a frequented 
track it is almost impossible to find an untouched 
plant of any kind. Cannon observed in Algeria 
that the Mzabite cemeteries, in which the domestic 
animals are not allowed to graze, form a place of 
refuge to plants which otherwise do not exist at all 
near the haunts of man. It is frequently stated that 
thorns (page 62) are produced as a defence against 
these browsing animals, and this explanation may be 
true in some places, but certainly does not fit the 
facts very generally. In favour of the defensive 
theory is the fact that in the Southern United States 
and in parts of Australia, where species of Opuntia 
(" Prickly Pear ") are used as food for sheep and 
cattle, only the thorny species can be successfully 
grown. If the thornless species are planted they 
must be protected by fencing against the grazing 
animals, and it is actually cheaper to grow the 
thorny species and to destroy the thorns by fire, 
when the plant is required for the stock, than to 
protect the thornless ones with fences. It is a fact 



RELATIONS OF ANIMALS AND PLANTS 137 

also that certain plants which are without thorns 
spring up in the midst of a thorny bush of another 
species : in the Algerian Sahara the Terebinth or 
Betoum tree (Pistacia) is shielded by the Zizyphus, 
and in the Indian desert the Zizyphus protects the 
grass Andropogon in a similar manner. It is 
generally supposed that the Terebinth and Andro- 
pogon are protected from grazers by the Zizyphus, 
but one must remember that any plant which suc- 
ceeds in estabhshing itself tends to shelter the soil 
around it, and to hold together the particles of soil 
if they are light and inclined to blow away. One 
well-established perennial plant mitigates the cUmatic 
conditions, and becomes the centre of a group of 
other plants of several species, and this wiU happen 
whether the perennial is thorny or not. It is possible, 
therefore, that the shelter which the Zizyphus affords 
from wind and heat is more important than the pro- 
tection which it gives from grazing animals. Against 
the theory that thorns afford protection from grazing 
animals one may advance the fact already quoted 
that near human habitations, or frequented tracks, 
aU desert vegetation, whether thorny or not, is 
stunted and deformed, or exterminated, because of 
the animals which graze upon it. From Central 
AustraHa we have Baldwin Spencer's evidence that 
the camel can eat every plant, from the spiny Acacia 
farnesiana to the juicy Claytonia. In the semi- 
deserts of Palestine camels prefer some of the more 
thorny shrubs, such as the Caper (Capparis), to others 
which are almost unarmed, but which are beheved 
to be bitter, or nauseating by reason of taste or 



138 ANIMAL LIFE IN DESERTS 

smell ; but Hart noted that they would eat Daemia, 
a very milky Asclepiad. I have seen goats at Jericho 
climbing up to browse on Zizyphus twigs though 
the spring herbage was up to their bellies. 

Furthermore, thorniness is most highly developed 
in the most arid deserts, exactly where large grazing 
animals are rarest, and the plants of the American 
deserts are on the whole more thorny than those of 
the Great Palsearctic Desert, though wild grazing 
animals are rare in the American deserts. 

The majority of the cacti are covered with long, 
straight thorns, which mice use as if they were 
rungs on a ladder ; the fruits (e.g. in Opuntia) carry 
small tufts of minute barbed hairs, which are easily 
detachable and very sharp ; these are thickly set 
on the fruit, and it might be supposed that they would 
form an efficient defensive mechanism, but this is 
far from being the case. In the American deserts, 
in which these plants are native, the squirrels and 
mice eat the fruits in great quantity. In the Old 
World, where Opuntia is an introduced plant, the 
rodents have learnt to climb the plants and steal 
the seeds. At Jaffa two species of the genus are 
cultivated : the fruit of one is eaten by man ; that 
of the other is opened by Gerbils (Gerbillus allenbyi), 
which gorge themselves and leave very few seeds 
to germinate. With the spiny fruit of Opuntia we 
may contrast the native and apparently defenceless 
gourd of Citrullus colocynthus, the Colocynth, which 
is not eaten by rodents or ruminants or jackals,! 
apparently because it is bitter and violently] 
purgative, and the Water Melon (C vulgaris), which 



RELATIONS OF ANIMALS AND PLANTS 139 

is even more defenceless, for it is neither bitter nor 
purgative, and yet it frequently escapes from 
cultivation and thrives without protection from man 
in India, Palestine, and doubtless other places. 

The conclusion to which these facts lead me is 
that thorns were not developed as a defence against 
grazing animals or rodents, and that they do not 
usually act in that way : I freely admit that they 
occasionally may exercise such a defensive function. 
They were probably developed in the first place as a 
response to the dry atmosphere. 



CHAPTER VII 
THE COLOURS OF DESERT ANIMALS 

There is no doubt that the colour of desert animals 
is in some way the result of the conditions under 
which the creatures hve, because it is quite char- 
acteristic of them, and not of animals from other 
types of country. Whether this colour is due to 
chmate or is protective we do not know, and I 
propose first to discuss the facts and then to examine 
a theory that has been brought forward to explain 
them. 

The majority of the animals which Hve in deserts 
are coloured buff, or sandy, or reddish-grey, and as 
plants are scanty and only very rarely cover the 
surface of the earth, we may say that generally the 
desert fauna resembles the ground on which it lives. 

Furthermore, the colour of the typical desert 
creature is imiform, without remarkable pattern on 
the upper surface. A few birds, such as the Horned 
Lark (Eremophila alpestris hilopha) and the Cream- 
coloured Courser {Cursorius gallicus) and a few 
Gazelles among the mammals, have blackish mark- 
ings on the head, but such a pattern is exceptional. 

Though the dorsal surface of most desert animals 
appears to a careless glance to be of one colour, 

140 



THE COLOURS OF DESERT ANIMALS 141 

when a specimen is examined closely it will often 
be found that the general unicolorous effect is 
produced by fine mottHng. In the Palsearctic 
region we have many examples of this ; among the 
birds the Egyptian Nightjar (Caprimulgus cBgyptius), 
many Sandgrouse (Fig. 34), especially females, Hey's 
and See-See Partridges (Ammoperdix) ; among the 
mammals several foxes and gerbik, in which a 
general sandy tone is produced by the presence of 
black hairs or black-banded hairs among the pale 
hairs ; many moths, especially Geometridse, in 
which a unicolorous appearance is produced by fine 
and inconspicuous banding or mottling ; in fact, 
fine vermiculation, producing a general impression 
of " self -colour," is common. 

In many desert mammals the under-surf ace is very 
pale or quite white. It is a fact that desert species 
and sub-species differ from their near relatives from 
other environments just as much in their pale 
ventral surface as in their buff or sandy backs. 
Moreover, the pale ventral area is often more 
enlarged up the flanks of a desert mammal than it 
is in its relatives from other environments. This 
paleness of parts of the animal which cannot normally 
be seen extends even to the sole of the feet : Sumner 
states that "the soles of the feet of desert deer-mice 
are nearly or quite lacking in pigment, while those 
of mice from the more humid coastal regions vary 
from purplish to nearly black." 

This type of coloration is found in all groups of 
animals which inhabit deserts ; in spiders and 
centipedes and wood-lice; in moths, bugs, beetles. 



142 ANIMAL LIFE IN DESERTS 

bees, flies, grasshoppers, and wasps ; in many lizards, 
and snakes ; in many birds of many different 
families, larks, finches, warblers, owls, partridges, 
nightjars, waders, and others ; in many mammals of 
many groups, rodents and insectivores, and bats 
and ungulates and marsupials. In fact, I cannot 
quote a single group of animals which lives in the 
desert and which does not furnish examples of this 
general truth. The only apparent exceptions are 
to be found in certain groups of beetles and other 
small Arthropods which Hve their whole Hfe below 
the surface of the ground. 

This type of colour and of pattern which we have 
come to recognize as characteristic of the fauna 
of deserts is not only widely distributed in the animal 
kingdom, but widely spread over the world. In 
any desert, in any of the five continents, you will 
find these sandy or buff birds and mammals and 
insects, and you wiU not find them in numbers in 
any environment which is not desert or semi-desert. 

Further, it may be stated that desert-dwelling 
animals are not coloured isabelline, or reddish buff, 
or greyish, indiscriminately ; for there is often a 
very close similarity in colour between the creature 
and the soil of the particular type of desert on which 
it lives. Thus, Lucas and Frost, in discussing the 
lizards collected by the Horn Expedition in Central 
Austraha, refer to the " presumably protective colora- 
tion of the species of diurnal habits. Many of these 
exhibit a very marked general rustiness, or even 
bright redness, in their general colouring, which is 
quite wanting in the forms met with in the South 



THE COLOURS OF DESERT ANIMALS 143 

and East, and which agrees well with the colour of 
the red sands upon which they were captured.'' 
These authors also quote Prof. Spencer's field notes 
made on the same expedition, with regard to an 
Agamid Hzard {Amphibolurus barbatus) : " On open 
country to south of Charlotte waters, a general 
yellow-brown colour — similar to general colour of 
ground, with withered grass, etc.," which is con- 
trasted with the series collected "at Crown Point, 
where plenty of red sand was, a peculiarly brick-red 
colour much resembhng the colour of the sandy hills 
close to the camp where it was found." It is 
particularly interesting to find that this species so 
closely resembles two different types of desert soil, 
for it is widely distributed in AustraHa, and by no 
means speciaUzed to a desert environment. The 
birds, too, furnish the most beautiful examples of 
species coloured so as to be well-nigh invisible 
among their native stones so long as they remain 
motionless. One of the Crested Larks {Galerida 
theklce) is represented by a dark race (G. t harterti) 
in the northern parts of Algeria, which are not 
desert ; in the semi-deserts which fringe the Atlas 
Mountains southwards this is replaced by a paler 
race {G. t. hilgerti) ; in the Northern Sahara itself 
a still paler race is found (G, t, deichleri), which " is 
so wonderfully adapted to the soil that it is easily 
overlooked if the birds do not happen to be on the 
wing or singing " (Hartert). Between Laghwat and 
Ghardaia a reddish form (G. t, carolince) of this 
species is found, and its distribution corresponds 
fairly closely with the reddish stony desert. The 



144 



ANIMAL LIFE IN DESERTS 



colour and distribution of these races finds its 
parallel in the hares, Lepus pallidior, which is pale 
and greyish and is found along the south side of 
the Atlas Mountains, and L. whitakeri, which is 
reddish sandy, and is found in the country round 
Ghardaia. Meinertzhagen has studied certain races 
of another species of Crested Lark {Galerida cristata) 
and arranges them thus, beginning with the darkest 
and ending with the palest. 



Race. 


SoiL 


Locality, 


Nigricans . 


Black alluvial 


Central Egyptian Delta 


Maculata . . 


Dark alluvial with a 






percentage of sand 


Cairo, Helwan 


Meridionalis . 


Dark brown, often red 


Crete 




Dark brown 


Cyprus 


Cinnamomina 


Reddish 


Beirut 




Brown 


Haifa 


Zion . . . 


Brown to pale brown 


Damascus, Tiberias, 
Jerusalem 


Brachyura 


Pale brown and sand 


Suez, Gaza, Sollum,etc. 



He quotes also the mean relative humidity and 
the mean rainfall of the locaUties, both for the year, 
and for the months April and May, when the birds 
are breeding. He concludes that " Crested larks 
are influenced in the colour of their plumage by 
protective resemblance to the soil on which they 
live, and that neither humidity nor rainfall has any 
effect on their plumage. This same influence seems 
to affect nearly all ground-birds which more or less 
live in the open, such as Ammomanes, Alcemon^ 
CEnanthe deserti, Eremophila, Alectoris, Pterocks, etc." 



THE COLOURS OF DESERT ANIMALS 145 

For reasons which I shall give later I am not 
convinced that the resemblance of birds to soil is 
" protective," if by that word it is implied that the 
resemblance affords protection from enemies, but 
let us accept it that there is a close similarity between 
the colour of the bird and the colour of its native 
soil. 

It is also interesting that in the first plumage 
these Crested Larks show very much the same 
differences in shade as do the adults of the same 
sub-species. The feathered young of G, c. brachyura 
is, for instance, paler than that of G, c, nigricans, 
and both of them are very much paler than specimens 
of G. c. cristata, the Central European race. 

A somewhat similar case is that of the Houbara 
Bustard. The typical sub-species {Chlamydotis u. 
undulata) inhabits the Sahara and Southern Morocco, 
and is of a mottled sandy colour, which accords 
well with the pale and sandy soil on which it Hves. 
In the Eastern Canary Islands (Fuerteventura and 
Lanzarote) the sub-species C, u, fuerteventurce is 
found : it differs from the typical sub-species in 
the speckling and mottling of its upper surface 
with black ; it harmonizes very closely with the 
lava-strewn wastes of these islands, and the typical 
pale race would be extremely conspicuous upon 
them. Accurate information with regard to the 
humidity of the air and the rainfall of these islands 
is lacking, but Bannerman attributes the blackening 
of the island race to its existence upon the blackish 
lava. 

It seems to be agreed among American zoologists 

L 



146 ANIMAL LIFE IN DESERTS 

that mice, wood-rats, and other small mammals 
which inhabit areas of blackish lava as well as other 
parts of the desert are often darker on the lava than 
elsewhere. It is fair to mention that this has 
recently been controverted by Sumner, who has 
shown that in some cases, at any rate, the darker 
colour may be due not to living on lava, but to 
differences in other environmental factors, such as 
rainfall. In the case of one animal (the deer-mouse, 
Peromyscus crinitus), he was able to show that if 
long series of this mouse living on black lava and on 
" pale grey, buff, and pinkish " rock were compared, 
no difference in tone could be detected either by eye 
or by photometer. 

Other cases occur in which the resemblance of 
animals which are, broadly speaking, " desert- 
coloured " to their particular type of desert, is by 
no means very close. I remember obtaining four 
species of mammalia at Qazvin in North- West 
Persia : the local fox was greyish sandy with a 
reddish saddle ; the hare was pinkish buff ; the 
gerbil {Meriones hlachUri lycaon) was yellowish buff ; 
and the dwarf hamster (Cricetulus) pure pale grey 
without any trace of yellow or buff colour. All 
these occurred on the same ground, and any one of 
them was a good example of " desert coloration," 
but none of them resembled the exact shade of the 
soil at all closely. 

In Mesopotamia downy young of the Sandgrouse 
Pterocles senegallus and P. exustus have been obtained 
in the same type of pebble and clay desert, but they 
differ widely both in pattern and colour. 



THE COLOURS OF DESERT ANIMALS 147 

Grinnell has recorded a similar phenomenon. 
Speaking of " conies " (Ochotona), by which an animal 
very different from the bibHcal cony or hyrax is 
meant, he says, " as elsewhere, the conies in the 
white momitains live in rock sUdes and broken-up 
rock out-crops." Two colours of rock occur in this 
range, a blackish or dark red ' shale,' and a white 
or greyish white granite. There are extensive belts 
purely of one or the other kind of rock. Our party 
took pains to shoot conies from each colour of 
ground, keeping notebook record of where each 
specimen was shot. I am unable to detect any 
difference in colour between animals shot from white 
granite and those from dark ' shale.' " 

Speaking of the Roadrunner {Geococcyx californi- 
anus), a large, ground-loving Cuckoo found in 
California, he remarks that "it is, of course, a 
remarkable exception if the Roadrunner, a terrestrial, 
permanently resident bird of all the areas it inhabits, 
should not show some geographic colour pecuHarities. 
Lideed, it is all the more strange that it does not show 
conspicuous differences in colour tone in the arid 
and subhumid areas it occupies, when we observe 
the remarkably different colour tones exhibited by 
the thrashers, towhees, spermophiles and jack 
rabbits of the same areas, these also being terrestrial 
animals. The Roadrunner's failure to conform to 
the rule offers a problem for those who would explain 
animal coloration whoUy on the ground of physio- 
logical response to meteorological conditions, irre- 
spective of adaptive value." 

Certain desert insects attain a silvery or sandy 



148 ANIMAL LIFE IN DESERTS 

appearance by being clothed with hairs of that 
colour ; many of these insects settle rarely or never 
on the desert soil, so that their case deserves special 
consideration. The phenomenon is found in many 
bees, wasps, and fossors, and in at least three 
famihes of flies (Bombyliidse, Nemestrinidae, and 
Tabanidae). That is to say that it has been evolved 
on a number of separate occasions to suit the particu- 
lar needs of insects that fly or hover over deserts. 
Morice was, I beheve, the first to call attention to it 
in Hymenoptera, remarking that " no one, I should 
think, who has collected in the deserts of Algeria, 
Egypt or Palestine can doubt that the very pale 
colours and shimmering silvery or golden pruinosity, 
so common in aU groups of Hymenoptera in such 
locahties, and practically there only, are cryptic 
characters, rendering the insects which possess 
them inconspicuous and almost invisible among the 
guttering sand and pale vegetation which they 
haunt. Here at least, contrary to the rule laid down 
by Wallace, we have stinging Hymenoptera coloured 
so as to resemble, or at any rate so as not to con- 
trast with, the inanimate and vegetable substances 
which normally surround them." I have quoted 
his words because they describe the facts excel- 
lently ; his suggestion that the colours are " cryp- 
tic " is a topic to which we shall return later. A 
similar condition prevails in the gad-flies (Tabanidae), 
many species of which from Mesopotamia and 
South Palestine are clothed with down of a pale 
tawny colour. This is remarkable, because the gad- 
flies rarely settle on the ground or on rocks except 



THE COLOURS OP DESERT ANIMALS 149 

at night, and spend most of the daylight hours 
visiting flowers or sucking the blood of the larger 
animals. Certain flies of the famiHes BombyUidae 
and Nemestrinidae exhibit the same type of colora- 
tion, though they spend their time at flowers or 
hovering in the air : they do not rest on the soil 
which they so closely resemble in colour. 

We find, then, that most of the animals which live 
in deserts are coloured buff or sandy or pale grey ; 
bold pattern is rare ; this type of colour is exhibited 
by animals of nearly every group, and is prevalent 
in the deserts of every continent. It is even char- 
acteristic of some insects, not closely related to one 
another, which spend the hours of daylight in the 
air or on flowers and not on the surface of the 
desert. As to the effect of these colours upon the 
human eye it must be acknowledged that the 
prevalent buff and sandy colours of desert animals 
do render them extremely difficult to detect, unless 
they move. This is probably as much due to their 
immobility as to their colour. Every naturahst 
who has ever visited the desert has noticed this, 
and it is true of all the manifold forms of life which 
exhibit these colours. The most remarkable exam- 
ple that ever came to my notice was in Baghdad, 
Mesopotamia, in September. There was a small 
patch of ground of perhaps an acre, walled off but 
not at that season cultivated. In it one could always 
be certain of flnding at least a score of Egyptian 
Nightjars {Caprimulgus cegyptius), but though the 
ground was absolutely bare, and though I visited 
the place repeatedly, I never succeeded in detecting 



150 ANIMAL LIFE IN DESERTS 

a Nightjar before it flew, and this in spite of the 
comparatively large size of the bird. We must 
admit it as a fact that the prevalent colour of desert 
animals does render them most difficult to see so 
long as they remain motionless. 

There is only one important exception to the 
generaHzation that desert animals resemble in colour 
the soil on which they live, but it is a most remark- 
able one ; in many deserts a number of the indigen- 
ous animals are black. This is not commonly 
known, but is none the less fact. Speaking generally, 
it may be said that any desert creature which is 
not coloured Hke its surroundings is black, for 
bright greens and blues and reds and yellows are 
very rare ; and though black animals are not a 
dominating element in the fauna, they are suffi- 
ciently numerous to be noticeable in many places 
in the Great Palaearctic Desert. The most remark- 
able group of black inhabitants of deserts are the 
Tenebrionidae, a family of beetles. Members of 
this family, to which the meal-worm (Tenebrio) and 
the Cellar Beetle (Blaps) belong, are found in a great 
variety of environments in nearly aU parts of the 
world. The majority of them are black, and 
nocturnal ; the habits and food of these insects are 
very imperfectly loiown, but it is beHeved that the 
larvae and adults of most feed on dried vegetable 
matter, and refuse generally ; possibly their abihty 
to live on dry food has enabled them to invade the 
arid areas of the globe. Whatever be the reason, the 
Tenebrionidae have proved successful in colonizing 
arid countries, and, as the following Hst shows, aU 




Fig. 42. — Typical Black Diurnal Tenebrionid Beetles of the Great Pal^arc- 
Tic Desert (x 4^). A. and B, Adesmia ulcerosa; C and D, Pimelia 
angulata. (E. Terzi.) 



THE COLOURS OF DESERT ANIMALS 151 

the large deserts of the world are inhabited by one 
or more of the many sub-famihes into which these 
insects are divided : — 

Sub-family. Desert inhabited. 

Erodiinae ..... Palaearctic 

ZophosinsB „ and African 

TentyriinsB „ „ „ 

Adesmiinae ..... ,, j, » 

Eurychorinae ..... South African 

Cryptochilinae ...... „ 

Molurinse ...... „ 

Sepidinse ..... Palaearctic and African 

Akidinae ...... 



.... ,, 

Pimeliinae ..... 



j> )> }> 



Blaptinae ..... „ ,j „ 

Eleodinae . . . . . American 

Praocinae ..... ,, 

Coniontinae ..... „ 

Adaliinae ..... Australian 

(K. G. Blair in litt.) 

Blackness, as I have said, is characteristic of the 
Tenebrionidae. The desert environment has not 
affected them, for in all the deserts in which they 
occur the majority of species remain black. As 
many of them are nocturnal, and as they shelter 
by day under rocks, this is not at first sight remark- 
able, but it is very remarkable that others have 
acquired a habit of wandering over the naked ground 
by day, and that these retain their uncompromising 
black colour. Examples familiar to the traveller 
in any of the deserts of Algeria, Egypt, Palestine or 
Persia are the genera Adesmia and PimeUa (Fig. 
42). These are large black active insects, and they 
are a dominant part of the fauna of these countries 
in winter, spring and early summer. Their activity 
is strictly diurnal, for they do not take refuge from 



152 ANIMAL LIFE IN DESERTS 

the midday sun, but retreat under stones at night 
and during cold weather. ^ As these insects are so 
numerous and so visible one naturally wonders how 
they protect themselves from insect-eating birds 
and lizards. It appears probable that they are to 
some extent saved from destruction by their size 
and their hardness : this is an inadequate protection, 
for the late G. Storey shot a young black and white 
Wheatear (species ?) in Wadi Hof, near Cairo, and 
found that it was stuffed with Adesmia, and Radde 
recorded long ago that the Red-footed Falcon 
{Falco vespertinus) eats Blaps and PimeHa on the 
Simferopol Steppes in April. 

The anomaly of the black colour and diurnal 
habits of these insects is heightened by the fact that 
some desert Tenebrionidse are dull brown, others are 
black and hairy, but they cover themselves with an 
earthy or dusty coating which is difficult to remove ; 
these inconspicuous Tenebrionidae are nocturnal 
insects, and it is difficult to see that their camouflage 
is of value to them. 

Black members of the Chafer family of Beetles, 
among them the famiUar " Scarab " of Egypt and 
other countries along the Mediterranean Httoral, 
occur in many places in the Great Palaearctic Desert, 
but they are neither so common nor so character- 
istic as the Tenebrionidae. Among the flies there are 
several species of Bombyhidse in the Great Palse- 
arctic Desert, which are black, or predominantly 
black. Fig. 43 shows a member of (a) the Bom- 

^ This statement is probably true of all species of Adesmia 
and of many Pimelise (e.g. P. angulata, Fig. 42) : other members 
of the genus are nocturnal. 




Fig. 43. — ^Typical Black Diurnal Flies, from Palestine, belonging to differ- 
ent SUB -FAMILIES OF THE BoMBYLiiD^ (x 4^). A, Bombylius fuscus (Bom- 
byliinse) ; B, Hemipenthes sp. (near H. velutina), (Anthracin^). (E. Terzi.) 



THE COLOURS OF DESERT ANIMALS 153 

byliinse, and (b) the Anthracinse, a sub-family in 
which this phenomenon is quite common. 

In the Algerian Sahara among the numbers of 
active black Adesmia one may frequently capture 
a large Long-horned Grasshopper, black and shiny, 
with red processes on the thorax. This insect is 
Eugaster guyoni. In contrast to the active Adesmias, 
it is a very sluggish insect and its hindlegs are not 
specially lengthened and strengthened for jumping 
as they are in nearly all its relatives. Further, we 
may suppose that Adesmia and the other diurnal 
Tenebrionidse are black by inheritance, and that 
they have retained the family's colours not because 
it was directly advantageous, but because it was not 
disadvantageous. No such reasoning can be appUed 
to Eugaster, which belongs to a family in which 
shiny blackness is extremely rare : we are therefore 
left to wonder at its assumption of this colour and 
at its abrogation of the power to jump. Eugaster 
is extremely conspicuous and deliberate in its 
motions ; when it is handled it pours forth a copious 
brown oily secretion, and it is tempting to suppose 
that this protects it from insect-eaters ; we have 
absolutely no evidence that this is the case. 

Among the Short-horned Grasshoppers (Locus- 
tidse or Acridiidae) there is an interesting species, 
CalUptamus coelesyriensis, which ranges from Pales- 
tine to Turkestan. In Palestine it occurs in semi- 
desert country among withered annual vegetation in 
the months of May and June. One common form 
is very dark chocolate brown all over, except that 
the ventral surface is slightly paler. I have nearly 



154 ANIMAL LIFE IN DESERTS 

always found it associated with much greater num- 
bers of a pale buff form of the same species ; inter- 
mediates between this and the chocolate form do not 
occur in my experience. It is remarkable that two 
varieties of one species, living in identical environ- 
mental conditions at the same season of the year, 
should be so differently coloured, the common form 
resembling the surrounding stones and dead herbage 
in colour, as do nearly all other members of the 
family, the rarer form being nearly black and very 
conspicuous. Another member of the same family 
{Poecilocerus bufonis) in Sinai is dimorphic in a 
similar manner. 

In most parts of the Great Palaearctic Desert, 
birds which are mainly or entirely blaick are found. 
Excellent examples are afforded by the Ravens and 
by a large number of species of black and white 
Wheatears and Chats (Saxicola). The latter range 
right across the Great Palaearctic Desert, from Rio 
de Oro and Morocco to Turkestan, Sind and Raj- 
putana. Inside the belt of desert and semi-desert 
they are abundant both as species or as individuals, 
and outside it they are rarer, and occur for the most 
part as stragglers. Blackness is not an ancestral 
colour for Wheatears and Chats, and is quite excep- 
tional among them. One can trace a progressive 
series among the desert members of the genus, 
showing the gradual replacement of buff by white, 
and then the replacement of the white by black. 

In some species the blackening has proceeded 
further in the male than in the female, in other 
species both sexes are equally black. It appears 



THE COLOURS OF DESERT ANIMALS 155 

therefore that these birds have evolved their 
blackness because in some way it fits them to a desert 
existence ; in this respect they resemble Eugaster 
guyoni and the dark form of Calliptarmos code- 
syriensis. This is the more remarkable because 
within the limits of the same genus (Saxicola) 
there are birds which inhabit the same deserts and 
which are coloured like the soil on which they live ; 
examples are the Isabelline Wheatear {8. isdbeU 
Una) and the Desert Wheatear {8. deserti), both of 
which are widely distributed in the Great Palae- 
arctic Desert, and occur side by side with various 
black and white congeners. The habits of the black 
and white Wheatears closely resemble those of the 
other members of the genus, that is to say that they 
are wary birds, given to perching on upstanding 
rocks and, at any rate to my eyes, easy to see when 
they are sitting still, and extremely conspicuous 
when they move. 

Among the reptiles there is one species which 
becomes increasingly black beneath as its habitat 
becomes more and more strongly desert. Hartert 
has recorded that the spiny-tailed Hzard ( Uromastix 
acanthinurus) of Biskra, El Kantara, and other 
places in the northern part of the Algerian Sahara 
is replaced farther south in the Mzab country by a 
form which is much blacker on its ventral surface, 
and that this in turn is replaced in Tademait and the 
central Sahara by a form in which the males are quite 
black, and the females nearly so, aU over the under 
surface of the body and the tail. This very remark- 
able case can scarcely be grouped with those which 



156 ANIMAL LIFE IN DESERTS 

we have already considered as the increased black- 
ness of the more desert forms of this species is con- 
fined to the invisible ventral surface. ^ 

I can find few records of the occurrence of black 
diurnal animals in any desert outside the Palsearctic 
region : it is possible that black animals occur and 
that no one has called our attention to them. It is 
interesting to notice that Merriam refers to the 
Tenebrionid genera Eleodes and Asima as common 
and characteristic in the Painted Desert, in America. 
Hudson speaks of Galictis barbara, a " quaint-looking 
weasel, intensely black in colour, and grey on the 
back and flat crown"; this animal is diurnal and 
hunts in companies on the pampas of La Plata. In 
the same country is found Didelphys azarce, a black 
and white oppossum : this animal is also diurnal. 
It is, of course, possible to suppose that these two 
totally unrelated conspicuous diurnal predatory 
animals exhibit " warning coloration," a topic too 
large to be considered here. 

I have summarized the facts ; let us now see 
whether they are capable of explanation. Many of 
us, during our childhood, were taken to the Natural 

1 Among the Amphibia and Reptiles which inhabit deserts 
there are species which develop brilliant colours in the wet season 
in such a way that they become extremely conspicuous. This 
brilliance reaches its climax after pairing has taken place, and 
is common to both sexes of the frog or lizard concerned. For 
details consult C. L. Camp, Notes on the Local Distribution and 
Habits of the Amphibians and Reptiles of South-Eastern California 
in the Vicinity of the Turtle Mountains, Univ. of California 
Publications in Zoology, XII, p. 511 (Aug. 12, 1916), and Baldwin 
Spencer, Report on the Work of the Horn Scientific Expedition 
to Central Australia, Part I, pp. 26, 27 (1896). 



THE COLOURS OF DESERT ANIMALS 157 

History Museum in Kensington, and shown the large 
case which illustrates desert hf e. We remember the 
sandy rocks, the sparse dry vegetation and the birds, 
beasts and reptiles all coloured so that they were 
inconspicuous. We did not reaHze that they were 
inconspicuous, at any rate in part, because they 
were motionless, and that about half the creatures 
in the case were strictly nocturnal. We were told 
that the animals were so coloured as a protection 
from their enemies, and most of us have grown up 
without ever critically examining this statement, so 
that the theory of protective coloration is still widely 
accepted by people who are not strictly scientists, 
but are very deeply interested in biological problems ; 
the time has come to examine it very closely. This 
theory presumes that there are predaceous creatures 
from which the animal must be protected, or else 
that the animal is itself predaceous and that its 
colour enables it to stalk its prey with success ; the 
theory presumes also that the protection given is 
actually effective under natural conditions in the 
open desert. One asks at once from what enemies 
the desert creature needs to be protected. Admit 
that the moths, grasshoppers, mantids, spiders, 
and other smaU organisms are preyed upon by 
insectivorous birds and reptiles, and suppose that the 
colour of these small animals gives them some 
measure of safety ; the supposition is not based on 
accurate knowledge, but it is not unreasonable. 
Now, what are the enemies of the larger "pro- 
tectively coloured " birds, the Sandgrouse (Pterocles) 
and Courser (Cursorius) ? 



158 ANIMAL LIFE IN DESERTS 

Falconers say that as a general rule trained 
Peregrines and Shahins cannot capture these birds 
except by chance, and that the ordinary desert 
Falcons, the Sakers and Laggers, are less swift than 
the Peregrines. It would seem, then, that the 
Coursers and Sandgrouse are protected from Falcons 
more by speed than colour. I know of no other 
predaceous animals which hunt by day and which 
may be supposed to chase Sandgrouse or Courser. 

The real enemies of these birds are probably cats 
and foxes and possibly jackals ; these aU hunt by 
night and by scent, so that the colour of the bird 
motionless in a dim light can hardly have a protective 
value to it. 

Now, let us consider the predaceous birds and 
animals — first those of diurnal and then those 
of nocturnal habits. The supporter of protective 
coloration supposes that they are coloured like the 
desert in order that they may more successfully 
stalk and seize their prey, that is to say that their 
colour effaces them. This ingenious explanation 
fails to cover the facts. The Merlin is fairly famihar 
to many of us as a small hawk, widely distributed in 
Europe and Northern Asia. It feeds largely on small 
birds and hunts on the wing ; any colour and pattern 
which is to prevent the small birds from seeing it 
should therefore be on the imder side of the bird. 
As a matter of fact, the ordinary western form of 
Merlin {Falco columharius regulus\ which does not 
breed in deserts, winters, among other places, in the 
deserts of Algeria, Tunisia and Egypt. Farther 
East, however, there is a race {Falco columbarius 



THE COLOURS OF DESERT ANIMALS 159 

pallidus) which breeds in the deserts and steppes of 
Central Asia ; this race is desert-coloured, being a 
very pale and dehcate blue-grey above, and paler 
beneath than the western race. The western 
Merlin, which is not desert-coloured, is well able 
to find a Hving in the deserts in which it winters ; 
on the supposition that the Merlin requires effacing 
coloration, why is it necessary for the eastern race 
to be coloured very pale, and particularly why should 
the colour of its upper surface be paler than that of 
the western race ? A good parallel is afforded by 
the larger falcons. The Peregrine {Falco peregrinus), 
which is not a desert-breeder and is dark iron-grey 
above, winters in many of the Great Palsearctic 
deserts ; in these regions one finds also the Saker 
Falcon (Falco cherrug) and the Lanner Falcon 
{F. biarmicus), which are pale desert-breeders. One 
cannot see that the desert species have any advantage 
over the Peregrine during the months during which 
they five side by side. 

With the Falcons the theory of protective colora- 
tion, or rather of effecting coloration, fails to cover 
the facts, but the effacing colour of other predaceous 
animals does help them to catch their prey. In the 
CaHfornian deserts near the Turtle Mountains there 
exists, according to Camp, a Rattlesnake (Grotalus 
cerastes) which is coloured so that when it Hes 
buried in sand flush with the surface it is well-nigh 
invisible. Invisibihty, or some close approach to it, 
really is attained, and the snake and the Hzards 
which form its prey are active by dayhght at a 
time when the value of colour as an effacer must 



160 ANIMAL LIFE IN DESERTS 

be at its highest. Instances such as this are few, 
and the theory of protective or effacing coloration 
which explains them well enough cannot be extended 
generally. 

In the case of nocturnal beasts and birds of prey 
it is still more difficult to explain colour as an effacer, 
because even by moonlight colour hardly exists, and 
differences between shades of colour are not appre- 
ciated. All the same, there is a large group of desert- 
coloured, nocturnal, predaceous forms, some hke the 
owls hunting by sight, others Hke cats and jackals 
and foxes by scent. All are pale in colour, and from 
numerous examples, occurring in aU deserts, I choose 
the following. Thomas has recently described a 
Caracal from Asben in the South Central Sahara. It 
differs from all known Caracals in its "exceptionally 
pallid coloration and silvery ears." It is "a desert- 
coloured form with whitish ear-pencils." Among 
the birds the Eagle Owl (Bubo bubo) is a wide-ranging 
species able to support itself equally in the forests of 
Scandinavia and the steppes and deserts of Persia, 
Transcaspia and Egypt. A large number of sub- 
species have been described and they form a most 
interesting gradation from the large dark forest 
birds of Europe and North- West Asia to such small 
and pale desert forms as Bubo b, aharonii in Southern 
Palestine ; B. b. ascalaphus in North Africa and 
Egypt ; B. b. turhomanus in Transcaspia, East 
Persia and Turkestan, and other forms. 

There is, of course, a stiU larger group of animab 
which are preyed upon and which are nocturnal. 
Nearly aU the Jerboas and Gerbils of the Old World, 



THE COLOURS OF DESERT ANIMALS 161 

and their counterparts in the American deserts and 
Australia (pages 74-80), are strictly nocturnal, and 
one may weU question whether their beautiful sandy 
tints have much protective value. By moonlight, to 
the human eye they appear nearly white and rather 
conspicuous. Most of them, it should be remem- 
bered, are very strictly nocturnal : Jerboas {Jaculus) 
and Dwarf Gerbils (Dipodillus) may occasionally be 
seen when the dayhght has nearly gone, but many 
other forms never come above ground until night 
has definitely faUen. In the summer and autumn 
of 1919 I was camped for four months outside 
Qazvin in the semi-desert of North- West Persia. All 
around us were the burrows of the Gerbils {Meriones 
blackleri lycaon and M, erythrurus), but never once 
did I see either of these animals by dayhght, either 
in the dawn or after sunset : every night I was in 
the desert between 8 and 9 p.m., and I always saw 
Gerbils crossing the beam of my lamp. Without 
a lamp I found it impossible to see them except when 
the moon was bright, and then they appeared white 
and conspicuous. Devout supporters of the theory 
of protective coloration claim that animals, both 
predators and prey, are rendered iaconspicuous even 
at night, perhaps by moonlight, by their pale colour ; 
the claim seems to me to be more ingenious than 
probable, but I cannot disprove it. The whole 
question of visibiHty at night, with or without moon, 
is beset with difficulties, because we have only the 
vaguest knowledge of the extent to which habitually 
nocturnal animals rely upon their eyes in obtaining 
their food. 



162 ANIMAL LIFE IN DESERTS 

The difficulty of accepting the view that pale sandy- 
tints " protect " the nocturnal animals of deserts, is 
as nothing compared with the difficulty of accepting 
the same view with regard to certain subterranean 
forms. The Pocket-Gophers (Thomomys) of the 
southern United States are found in a variety of 
environments, including the deserts. They very 
rarely come above ground, but none the less those 
that live below the surface of the desert are paler 
than the others ; the palest of all is Thomomys 
alhatus described by Grinnell from the Imperial 
region of California. This form is actually the 
palest of all the animals of its native region ; and 
all the mammals of the Imperial region, which 
is desert but not of an extreme sort, are very 
pale. It is interesting to learn that the soil in 
which this Pocket-Gopher burrows is by no means 
very dry. 

The Marsupial Mole (Notoryctes), which is a purely 
subterranean inhabitant of sandy places in Central 
Australia, is pale sandy, frequently almost white, in 
colour. It is even more rarely exposed to dayhght 
and to enemies on the surface of the soil than the 
Pocket-Gopher, and unless we postulate that both 
are descended from ancestors which Hved on the 
surface of deserts and there acquired a " protective 
coloration," we cannot in any way accoiuit for their 
colour : for such an hypothesis there is not a shadow 
of evidence. 

Similar examples occur among the Reptilia. The 
Sand Boa {Eryx jaculus) and the nearly Kmbless 
Skink {Eumeces scutatus) are animals which live 



THE COLOURS OF DESERT ANIMALS 163 

nearly all their lives underground : they are certainly 
paler and less distinctly marked when they Hve 
in the soil of deserts than when they live in the soil 
of wooded country, as my friend Capt. C. M. 
Ingoldby informs me. 

It is generally true that bats of desert areas are 
paler above and below than their relations living in 
areas which are not desert. Many examples might 
be chosen from Persia, Mesopotamia, Egypt, and the 
American deserts to show that this diiference is the 
rule. This very general truth hardly admits of an 
explanation as an example of "protective colora- 
tion," for predaceous enemies of bats must be rare ; 
and in any case they do not pursue the bat against 
a background of desert soil. The most likely 
enemies are owls, but in the Great Palaearctic Desert 
owls are on the whole not common, except the Little 
Owl (Athene noctua subspp.), which hunts in the dusk 
rather than at night and is not a serious enemy of 
the bats. From what enemy, then, are the bats 
" protected," and if a predaceous enemy exists does 
their protection not He rather in their speed and 
agility than in their colour ? 

I have endeavoured to show that the theory of 
protective coloration breaks down when we consider 
particular animals with reference to their prey or 
their predatory enemies. There are other instances 
in which the animal's colour should apparently give 
perfect protection were it not that its habits are 
unsuitable. 

One must realize that colour assimilating perfectly 
to the natural environment will give little protection 



164 ANIMAL LIFE IN DESERTS 

unless the animal remains stiU. Abel Chapman has 
gone so far as to state it as an axiom that " absolute 
immobility, on the part of the object itself, is 
essential ; to put it in other words that the slightest 
movement, even of a part, is fatal to the value of 
any protective principle." I think few of us would 
agree to so extreme a statement, but every field 
naturaUst knows that it is movement which catches 
the eye more readily than colour, or pattern or even 
symmetry. The Cream Coloured Courser {Cursorius 
gallicus) is as perfect an example as one could find of a 
bird which is invisible in desert, so long as it is still ; 
sometimes it crouches and then it defies detection 
in stony desert at 20 yards. More often it does not 
crouch when you approach it, but gets on its long 
legs and runs rapidly away ; it stands high above 
the ground, casting a conspicuous black shadow in 
the bright sunlight, and trusts to its legs and not 
to its colour to ensure its safety. Even when it is 
not disturbed the Courser is very conspicuous when 
feeding in the early morning and late evening : as the 
sun is low it casts a particularly large shadow, so 
that at these times the bird is easy to see. The same 
may be said of many other desert birds which are 
beautifully "protected" if you see them in a 
museum, but are quite conspicuous in nature 
because they do not keep stiU. Most of the larks 
of the Great Palaearctic Desert (Ammomanes, Gale- 
rida and others) are rather fooHsh Httle birds which 
scratch and feed and chirrup within 20 yards of you, 
and you can only feel that a Httle ordinary intelligence 
would render them invisible. Hey's Partridge {Am- 



THE COLOURS OF DESERT ANIMALS 165 

moperdix heyi) and the See See (A. griseogularis) 
are two small Partridges with exquisite soft buff and 
greyish sandy feathers. All through the middle of 
the day they lie up in holes in rocks and under 
boulders : at the time they are, of course, invisible 
owing to their position, not their colour. When the 
sun is low they come out to feed ; though their legs 
are short their shadow is long at this time of day, 
and they are quite conspicuous. 

In certain grasshoppers it seems probable that 
the coloration is actually protective. Vosseler men- 
tions the Short-horned Grasshoppers Eremobia, 
Eremocharis, Pamphagus and others, in all of which 
the thorax and abdomen are widened and flattened 
in such a way that the animal is triangular in 
transverse section and flat below. When it presses 
its ventral surface to the ground there is no shadow 
to betray it, and while at rest it carries the broad 
flat femora pressed against the abdomen, thus 
contributing to the same result. In this attitude 
every visible part of the insect is "desert colour," 
and is roughened so that it resembles rough rock or 
sand : bright colours occur on the hind-wings, on 
the inner face of the femora, and on intersegmental 
membranes, but they cannot be seen while the 
insect is at rest. It seems, then, that in these 
grasshoppers shape, colour, surface sculpturing and 
habit co-operate to render the insect difficult to 
see, and one must admit that in these cases the colour 
is protective, for it is unreasonable to argue that the 
shape, sculpturing and habit are protective, and 
that the colour with which they co-operate is due to 



166 ANIMAL LIFE IN DESERTS 

some other cause. Such cases as this are rare, and 
I maintain that the theory of protective coloration 
does not cover more than a few of the phenomena. 
For instance, among the invertebrata one may find 
examples of colour which would conceal an animal 
were its habits not faulty. The hovering flies and 
bees and wasps to which reference has already 
been made (page 148) are a case in point ; so are 
many grasshoppers which climb on a stone and 
rub their legs together to make a noise, thereby 
betraying their position by their noise and move- 
ment. 

I think, then, that we are justified in saying that 
many creatures whose colours would afford them 
complete protection if they kept still are rendered 
easy to see because their movements annul this 
protection : if the colour has a " protective func- 
tion," then the habit has an " advertising func- 
tion " : a theory of advertisement might be launched, 
and could be almost as well supported as the more 
popular theory of protection. 

And then how many colours there are which we 
must frankly say are unsuitable, unless we discard 
the theory of protective coloration. I have dealt 
at some length with the black forms earUer in this 
chapter : let us now consider them from the point 
of view of theory. Enthusiastic supporters of 
" protective coloration " have realized that a black 
and white Wheatear perched on a rock might raise 
doubts as to the soundness of that theory, and they 
have urged that these birds are not really conspicu- 
ous in a bright sun, among dazzling high Hghts and 



THE COLOURS OF DESERT ANIMALS 167 

black shadows, so long as they remain still ; un- 
fortunately Wheatears are active, restless birds and 
do not remain still for long. If we grant, what no 
one who knows these birds in their haunts will 
deny, that they are very easily seen, we may sup- 
pose that they are protected from diurnal birds of 
prey by their extreme wariness. This might aboUsh 
the need for protective coloration, but does not in 
the least explain the assumption of black, or black 
and white colour. 

Remember, also, that the black, or black and 
white Wheatears exist side by side with buff and 
isabeUine congeners, and the nearly black race of 
Calliptamus ccelesyriensis, so far as we know, never 
replaces the normal buff typical race of its own 
species. The buff and black exist side by side and 
appear to fill identical places in the general economy 
of nature. 

It is this recurrence of blackness, in widely 
separated groups of animals, which is so remark- 
able. If we may postulate that the Raven has 
no predaceous enemies, that Eugaster (page 153) 
is protected by its oily secretion from whatever 
enemies it has, and that the Wheatears evade the 
hawk by quickness and watchfulness, then we can 
understand that desert-colour is not necessary to 
these animals. But at once we are faced with their 
imanimous choice of black : if they are freed from 
the necessity of being buff, why are none of them 
green, or red, or blue ? We must remember that 
black absorbs more radiant heat than any other 
colour. Presumably therefore a black creature must 



168 ANIMAL LIFE IN DESERTS 

evaporate more water than a similar buff creature, 
if it is to keep its body temperature below a certain 
figure on a particular day. This, one would sup- 
pose, would severely handicap the black creatures 
under circumstances in which water is extremely 
scarce. 

And then, again, why in particular do Eugaster 
and CalUptamus coelesyriensis and the Wheatears 
become black, for it is against their family tradi- 
tions ? The Raven and Tenebrionids and the 
Scarab, we may suppose, are black because the 
colour is ancestral and they found no reason to 
alter it ; but the Eugaster and CalUptamus and 
Wheatears have broken with aU tradition, and at 
present we cannot explain their blackness. 

I maintain, then, that protective coloration cannot 
be accepted as a theory to explain the very remark- 
able coloration of desert animals. It is not easy 
to apply it to animals which hunt or are hunted 
at night ; or to animals which appear to be without 
any large enemies more powerful than themselves, or 
to animals whose paUid colour extends to their beUies 
and the soles of their feet. It cannot be appHed at aU 
to subterranean animals, nor to black animals, nor to 
those whose colour would protect them if their 
habits were radically altered. I do not deny that 
protection is afforded by colour, under certain cir- 
cumstances, to certain animals : on the contrary I 
readily admit that many desert animals are rendered 
invisible by their colour, which harmonizes per- 
fectly with their particular environment : most of 
these animals are invertebrates and not rapid in 



THE COLOURS OF DESERT ANIMALS 169 

their movements : to these forms the theory of 
protective coloration may rightly be applied. The 
point upon which I wish to insist is that the theory 
only covers a small portion of the facts ; we must 
look for some other cause, and suppose that after 
the prevalent buff or sandy colours had become 
estabhshed, certain of the creatures used them as 
a protection from their enemies : this is equivalent 
to saying that the protection afforded is quite a 
secondary matter and in no way causal. 

If we are compelled to disavow our faith in pro- 
tective coloration as the cause of this remarkable 
general depigmentation, to what are we to turn for 
an explanation ? The cause is one which affects 
animals of every type, in every desert ; it does not 
discriminate between prey and captor, between the 
creeping and flying animals, between the diurnal, 
the nocturnal, and the subterranean. It is so 
universal in its appHcation that it is probably 
physical. No biological agency, such as the struggle 
with rivals for food or water, the avoiding of enemies, 
or seeking a mate, can cover so wide a range of 
animals ; heat alone it is not, for heat in other 
parts of the world does not produce these uniform 
pale forms ; low or fluctuating relative humidity 
it can hardly be, for the animals which live below 
stones and in burrows by day, and emerge at night, 
are not exposed either to very low or very fluctu- 
ating humidity. I am unable to suggest any con- 
dition, or combination of conditions, which can 
make itseK felt so widely, but I feel that the 
explanation will eventually be found in studying 



170 ANIMAL LIFE IN DESERTS 

the effects of physical conditions upon the animal 
life, and that no progress is possible until we rid 
ourselves of our belief in protective coloration, at 
any rate so far as it is appUed generally to desert 
animals. 



INDEX 



Aciwjia, 137 

Acanthodactylus, 118, 130 

AdaliinsB, 151 

Addax Antelope, 89 

Addra Gazelle, 89 

Aden, Arabia, 20 

Adesmia, 151-153 

Adesmiinae, 161 

Africa, S.W., 4 

Agama, 92, 98 

Agriophyllum, 128 

Akidinse, 151 

Alaemon, 87, 144 

Alectoris (Caccabis), 49, 144 

Algiers, Africa, 32 

AUactaga, 76, 79, 80 

Amara, Mesopotamia, 13 

America, desert reptiles of, 92, 99 

America, N., deserts of, 3, 103, 115, 

161 
America, S., deserts of, 4 
Ammi, 124 

Ammomanes, 87, 111, 112, 144, 164 
Ammospermophilus, 89 
Amphibolunis, 143 
Amu Darya, Turkestan, 51 
Amydrus, 49 
Anderson, 126 

Anderson and De Winton, 117 
Andijan, Turkestan, 13 
Animals, coloration of, 140-170 
Animals and drought, 81-92, 127 
Animals and heat, 98-108 
Annual plants, 57-58, 123-125 
Antechinomys, 78-80 
Anthia, 130 

Ants in deserts, 71-72, 83, 103 
Ants, honey-pot, 72, 120 
Ants, sand-dwelling, 119-120 
Ant-chat, 112 

Apterous insects in deserts, 113 
Apus, 94-95 
Apus {see Cypselus) 
Arabia, 49-50 
ArctiidsB, 114 
Arctotnys, 134 



Artemia, 95 

Asphodel, 59, 126 

Astacopsis, 96 

Athene, 104, 163 

Atkinson, 81 

Atriplex, 45, 64, 100, 127 

Augidras, 21, 28, 43, 88 

Australian deserts, 6, 12, 73, 92, 95, 

96, 98, 100, 101, 104, 116, 137, 

142, 143, 161 
Available moisture, 14 



Babylon, Mesopotamia, 16 

Bagdad, California, 11 

Baghdad, Mesopotamia, 7, 12, 17, 

19 
Bahrein, Persian Gulf, 7, 20 
Bairam Ali, Turkestan, 13 
Balud Ruz, Mesopotamia, 30 
Bannerman, D., 145 
Base -levelling, 66 
Basra, Mesopotamia, 12, 13 
Bateson, W., 134 
Batin, Arabia, 50 
Bats, 83, 87, 104 
Beaucamea, 61 
Bees, 67 
Belenois, 69 
Beni Ounif, Algeria, 12 
Birds' eggs, 105-107 
Biskra, Algeria, 72, 73, 129, 155 
Blaps, 104, 150, 152 
BlaptinsB, 151 

Blatter, E. and Hallberg, F., 40, 48 
Bombyliidse, 148, 149, 162 
Boreida, Arabia, 43 
Brine-Shrimp, 95 
Bubo, 104, 160 
Bucanetes {see Erythrospiza) 
Bulbul, White-cheeked, 74 
Bullfinch, Trumpeter, 86, 111 
Bunting, Striated, 86 
Burrowing animals, 102 
Bustard, 87, 145 
Butterflies, Blue, 110 
Butterflies in Mesopotamia, 67 



171 



172 



INDEX 



Caccabis {see Alectoris) 

Cactus family, 60-63, 128, 135, 138 

Cactus, Giant, 62, 131, 132, 135 

Cahuilla, California, 31 

Calexio, California, 9 

Callegonium, 110 

Calliptamus, 153, 167 

Callisaurus, 118 

Calotropis procera, 61 

Camel, 88, 99, 137 

Camp, C. L., 117, 166, 169 

Camponotus, 72 

Cana, F. R., 43 

Canary Islands, 145 

Cannon, W. A., 31, 136 

Caper bush, 68 

Capparis, 68 

Caprimulgus, 141, 149 

Carabidse, 104, 113 

Caracal, 160 

Caspian Sea, 62 

Caterpillars and wind, 114 

Caves, 48, 49, 104, 105 

Centunis, 132 

Ceramodactylus, 118 

Cerastes, 130 

Cercomela, 112 

Cereus, 62, 131, 132, 135 

Chaman, Baluchistan, 7, 18 

Chapman, Abel, 89, 112, 164 

Charadrius, 108 

Chilades, 68, 111 

Chiroleptes, 97, 98 

Chlamydotis, 87, 145 

Chough Thrushes, 87 

Chuckwalla, 98 

Cinnyris, 134 

atellus, 89, 115 

atruUus, 55, 135, 138 

aay Desert, 37, 44 

Clay, desert, saltness of, 45, 46 

Closed basins, 51 

Colchicum, 59 

Coleoptera, wingless, 113 

Colias, 67 

Colocyiith, 55, 138 

Coloration of animals, 140-170 

Columba livia, 105 

Coney, 49 

Coniliunis, 77-80 

ConiontinsB, 151 

Corvus, 49 

Courser, Cream-coloured, 86, 107, 

140, 157, 164 
Cricetulus, 146 
Crickets, 66, 103, 113 
Crocus, 59, 126 
Cro talus, 159 
CryptochilinsB, 151 



Ctenomys, 116 

Cursorius, 86, 107, 140, 157, 164 

Cypselus, 104 



Date Palm, 42, 135 
Date Palm, fauna of, 102 
Dead Sea, Palestine, 46, 52 
Death Valley, America, 52 
Dera Ismail Khan, India, 8 
Desert, Great PalsBarctic {see Great 

Palsearctic Desert) 
Desert Quail, 87 
Desert soils, 36-50 
Desert Warbler, 83 
Deserts, definition of, 2 
Deserts, extent of, 3 
Deserts, temperature of, 16-22 
Deserts, watercourses in, 49-51 
Dew, 14, 81 
Didelphys azarce, 156 
Dipodillus, 77, 79, 103, 127, 161 
Dipodomys, 79, 103 
Dipodops, 103 
Dipus, 75-80 
Doughty, C, 43, 88 
Dragon-fly, 94 

Drought, effect on mammals, 73 
Ducrosia, 124 

Dunes, sand and rainwater, 41 
Dust -devil, 29 
Dust-Mulch, 39 

E 

Echinocactus, 62, 135 

Echinops, 128 

Eggs of desert birds, 105-107 

Egypt, 126 

Eland, 89 

El Arish, Sinai, 20 

Eleodinse, 151 

El Paso, Texas, 12 

El Wed, Algeria, 32, 42 

Emberiza, 86 

Ephydridse, 94 

Eremiaphila, 99 

Eremobia, 165 

Eremocharis, 165 

Eremophila, 111, 140, 144 

Erodinse, 151 

Erythrospiza, 86, 111 

Eryx, 162 

Estheria, 94 

Eublepharis, 92 

Eugaster, 153, 155, 167, 168 

Eumeces, 162 

Euphorbiaceae, 60 

Euphrates, River, 50, 51 

Eurychorinse, 151 



INDEX 



173 



Evans, W. E., 65 
Evaporation, 30-33 



Falco (Falcon), 133, 162, 168, 169 

Fennec Fox, 116 

Fischeria, 99 

Floods, 50, 96 

Flycatcher, 133 

Foeniculum, 124 

Forbes, R., 10 

Fort Mohave, Arizona, 9 

Fossors, 67 

Fox, 116, 127, 146, 158 

Francolinus, 87 

Fresh -water fauna, 93-98 

Frogs, Australian, 95-98 

G 

Galerida, 86, 130, 143, 144, 164 

Oalerida cristatay first plumage, 145 

OalicUs barbara, 156 

Gazelle (Gazella), 89, 99 

Oeococcyx califomianus, 147 

GeometridsB, 141 

Gerbil, 77-80,102, 138, 146, 160, 161 

Gerbillus, 77, 79, 80 

Ghardaia, 17, 18, 31, 32, 143 

Giant Cactus (see Cactus) 

Giraffe, 89 

Gizeh, Egypt, 24 

Goats eating Zizyphus, 138 

Gobi Desert, China, 20 

Golodnaia Steppe, Turkestan, 13 

Gopher, 162 

Graphipterus, 130 

Grasshoppers, Long -horned, 113,153 

Grasshoppers, Short-homed, 99, 
113, 153, 165 

Gravel desert, 48 

Grazing animals, 136 

Great Palsearctic Desert, 3, 6, 41, 
47, 59, 89, 100-104, 110, 123, 
135, 138, 150, 152, 154, 163 

Great Salt Lake, Utah, 52 

Gregory, J. W., 88 

Grinnell, J., 115, 131, 132, 147, 162 

Ground Squirrel, 89, 116 

Gryllidse, 103 

H 
Hamster, 146 
Hare, 99, 127, 144, 146 
Hare, Cape Jumping, 78 
Harrison, L., 98 
Hart, E. C, 126, 138 
Hartert, E., 10, 42, 72, 111, 129, 

143, 165 
Haywood, A. H. W., 10, 88 
Hedin, S., 44 



Heleioporus, 97 

Heliotropium, 110 

Helwan, Egypt, 16 

Hemiechinus, 83 

Hermetia, 92 

Hibernation in desert insects, 71 

Hingston, G. W. G., 92 

Honey -pot Ants, 72, 120 

Hornet, 87 

Himiidity, 22-27 

Humus, scarcity of, 36, 41 

Hyla, 96 

Hymenoptera, 66, 87, 125, 148 

Hypocolius ampelinus, 136 

Hyrax, 49 

I 

Imperata, 110 

Indian Desert, 7, 8 

Indio, California, 11 

Ingoldby, C. M., 92, 163 

In Salah, Sahara, 19 

Insect eaters, rarity of, 79, 83 

Insectivora, 83 

Insects, seasonal abundance of, 65- 

73 
Ipomsea, 61 
Iris, 59, 126 
Isidorella, 95 



Jackals, 135, 138, 158 

Jacobabad, India, 18 

Jaculus, 75, 76, 79, 80, 90, 103, 161 

Jaffa, Palestine, 42 

Jaisalmer, India, 8 

Japyx, 101 

Jaxartes, River, 51, 52 

Jerboa, 74, 82, 102, 160, 161 

Jericho, Palestine, 57 

Jodhpur, India, 13 

Jordan Valley, Palestine, 6, 46, 52 

K 
Kangaroo Rat, 115 
Karachi, India, 8 
KasaUnsk, Turkestan, 17 
Kidal, Sahara, 10 
Kit Fox, 116 
Kobelt, 134 
Kufara, Libya, 10 



Laghwat, Algeria, 31, 32, 143 

Lake Eyre, Australia, 52 

Lanius, 100 

Larinus, 129 

Larks {see Alsemon, Ammomanes, 

Galerida, Rhamphocorys) 
Lasiocampidse, 114 



174 



INDEX 



Lava, fauna of, 145-146 

Lepus, 127, 144 

Libyan Desert, 11, 33, 48, 109 

Light, 33 

Limnodynastes, 96 

Liparidae, 114 

Livingston, B. E., 39 

Lizards, Sand-dwelling, 117-119 

Loess, 41, 44, 46 

Lophortyx, 87 

Loranthus, 134 

Lucas and Frost, 142 

Luxor, Egypt, 22 

Lycium, 125 

Lymantriidse, 114 

M 
MacDougal, D. T., 4, 55, 56, 61 
Mandali, Mesopotamia, 86 
Mantis Family, 66, 99, 113 
Marmot, 134 

Meade-Waldo, E. G. B., 84, 107 
Meinertzhagen, R., 144 
Melophorus, 72 
Menjil, Persia, 28 
Meriones, 77, 79, 92, 130, 146, 161 
Merlin, 158 
Merriam, C. H., 156 
Mesopotamia, 46, 65, 70, 71, 90, 92, 

102, 103, 124, 127, 135 
Micropallas, 132 
Mohammerah, Persia, 25, 26 
Mqhave, Arizona, 12, 31, 32 
Mdle, Marsupial, 162 
Mole-rat, 126 

Mollusca in Australian deserts, 95 
Moloch, 92 
MolurinsB, 151 
Montgomery, Punjab, 8 
Morice, F. D., 148 
Mosquitoes, 94 
Mosul, Mesopotamia, 17, 26 
Mouse, House, 102 
Mouse, Spiny, 102 
Multan, India, 8 
Mus, 78, 102 
Myiarchus, 133 
Mjrmecobius, 83 
Myrmecocystus, 72 
Mzabite cemeteries, 136 

N 
Nefud, Arabia, 43 
Nemestrir^idsB, 148, 149 
Nesokia buxtoni, 103 
Nettles mark camp sites, 134 
Newt, 93 

Nightjar, 141, 149, 150 
Nile, River, 61, 108 



Normand, C. W. B., 29 
Notomys, 77, 79, 80 
Notoryctes, 83, 116, 162 
Nukus, Turkestan, 18 



Oasis, 54, 55, 74 
Ochotona, 147 
(Edicnemus, 86 
CEnanthe {see Saxicola) 
Onion, 59 

Oodnadatta, Australia, 12 
Opuntia, 136, 138 
Oran, Algeria, 32 
Omithogallum, 59 
Orthoptera, 66, 112 
Oryx Antelope, 89 
Ostrich, 89, 105, 106 
Otus, 133 

Owl, Eagle, 104, 160 
Owl, Elf, 132 
Owl, Little, 104, 163 
Owl, Screech, 133 
Oxus, River, 51, 52 



Palaearctic Desert {see Great False - 

arctic Desert) 
Palestine, 20, 42, 47, 102, 103, 114, 

126, 128, 148, 151, 153 
Parnphagus, 165 
Panicum, 110 
Papilio, 124 
Pamara, 68 
Partridge {see under Alectoris, Am- 

moperdix, Francolinus) 
Passer, 100 
Paulsen, O., 19, 41 
Pedetes, 78-80 
Peile, H. D., 124 
Perognathus, 79, 80 
Peromyscus, 146 
Persia, 161 

Petroalexandrovsk,Turkestan, 1 7, 20 
Phascogale, 73, 78-80, 125 
Philby, H. St. J., 50 
Phoenix, 135 
Phrynocephalus, 118 
Phyllopoda, 94 
Pieris, 67 

Pigeon, Rock, 49, 105 
Punelia, 151, 152 
PimeUinsB, 151 
Pistacia, 137 
Pitman, R. B., 103 
Piute Dam, Utah, 31 
Plover, Kitlitz, 108 
Pocock, R. L, 117 
Podoces, 87 
Poecilocerus, 154 



INDEX 



176 



Polygonum, 110 

Porcupine, 49 

Port Said, Egypt, 7 

Praocinse, 151 

Pratincole, 105, 107 

Predaceous animals, 168-160 

Prezhevalsky, 20 

Prickly Pear, 136, 138 

Procavia, 49 

Proctor, J., 119 

Prosopis, 125 

Protective coloration, 146, 148 

Protaetia, 129 

Protozoa of sand, 121 

Pterocles, 84, 144, 146, 157 

Pulicaria, 110 

Pycnonotus, 74, 100 



Q 



Quail, Desert, 87 

R 

Raczkowski, 46 

Rain, effects of abundant, 72, 74 

Rainfall, 6-14 

Rainstorms, 13, 60 

Rajputana, India, 48 

Rattlesnake, 159 — 

Raven, 164, 167, 168 

Rhamphocorys, 111 

Roadrunner, 147 

Rock Desert, 48 

Rock Doves, 49, 105 

Rodents in S. Palestine, 126 

Roebum, Australia, 12 

Rohlfs, 19 

Rothschild, W. (Lord), 111 

Ruby Wasps (Chrysids), 67 

Ruta, 124 

S 
Sahara, 19, 32, 42, 43, 47, 72, 111, 

112, 129, 137, 143, 145, 165 
St. George, Utah, 9 
Salsola, 55, 127, 129 
Salton Sea, Arizona, 12, 62 
Salts found in deserts, 46, 46 
Sand desert, 40 
Sand desert, fauna of, 116-121 
Sand-dwelling Protozoa, 121 
Sandgrouse, 84, 105-107, 128, 146, 

169 
Sauromalus, 98 

Saxicola, 49, 100, 112, 130, 154, 155 
Scaptira, 118 
Scarab, 162, 168 
Scarturus, 76, 80 
Schimper, 136 
ScincidflB, 117 
Seeds, spiny and hooked, 135 



Semi-deserts, definition of, 2 

SepidinsB, 151 

Shakespear, 50 

Shamal, 27 

Shrike, Great Grey, 100 

Silt, 44 

Silvery insects in deserts, 148 

Sirocco, 27 

Sminthopsis crasaicaudata, 73 

Soil, relationships with, 114-121 

Soil, temperature of, 20-22 

Soils, water capacity of, 37-39, 44 

Spalax, 126 

Spalding, V., 135 

Sparrow, House, 100 

Spencer, B., 73, 74, 95, 101, 126, 

137, 143 
Spurge Family, 60 
Squill, 69, 126 
Squirrel, Ground, 89, 115 
Star of Bethlehem, 59 
Stenodactylus, 118, 130 
Stone and earth desert, 47 
Stone Curlew, 86 
Stones, animals living imder, 100- 

102 
Storey, G., 152 
Su8Bda, 45, 66, 127 
Succulence, 60-62 
Sudan, 17, 112 
Sumner, F. B., 141, 146 
Sunbu-d, 134 

Swallow-tail Butterfly, 124 
Swifts, 104 
Sylvia, 83 

Syr Daria, Turkestan, 61 
Syrrhaptes, 128 



Tabanidas, 94, 148 

Tachta, Turkestan, 19 

Takla Makan, China, 43 

Tanezruft, Sahara, 88 

Tarucus, 67, 111 

Tashkent, Turkestan, 7, 17, 20 

Taterona, 77 

Telphusa, 95 

Temperature, daily range of, 19 

Temperature, extremes of, 17 

Temperature, monthly average, 16 

TenebrionidsB, 104, 113, 130, 150- 

153, 166, 168 
TentyriinsB, 151 
Teracolus, 68, 69 
Teratoscincus, 118 
Terebinth, 137 
Thomas, H. H., 48, 109 
Thomas, O., 160 
Thomomys, 162 
Thomson and Thomson, 121 



176 



INDEX 



Thominess, 62, 136-139 
Ticehurst, C. B., 74, 86, 106 
Tidikelt, Sahara, 10 
Tigris, River, 60, 61, 65 
Tiliqua, 100 

Toes, reduction of, 74-76, 80 
Traganum, 10 
Transcaspia, 46, 50, 52 
Treefrog, 96 
Tripoli, Africa, 19 
Tristram, H.B., 126 
Tristram's Grackle, 49 
Tucson, Arizona, 9, 12, 22, 31 
Tulip, 59 
Tuomey, 131, 135 
Turkestan, 46 



U 



Urginea, 126 
Uromastix, 155 
Utah, America, 52 



Vegetation, annual, 57-58, 123-125 
Vegetation, perennial, 68-62, 125- 

133 
Vespa, 87 
Volga, River, 62 
Vortex, 29 
Vosseler, 165 
Vulpes {see Fox) 



W 

Wadi Dawasir, Arabia, 50 

Wadi Haifa, Egypt, 16, 17 

Wadi Hanifa, Arabia, 50 

Wadi Rummah, Arabia, 49, 50 

Wadi Solaf, Sinai, 50 

Warbler, Desert, 83 

Wargla, Algeria, 12, 19 

Wasps, 67 

Watercourses, 49 

Water Melon, 138 

Water Supplies, 81 

Wheatears (Saxicola = (Enanthe), 

49, 167, 168 
Wheeler, W. M., 71, 120 
Wild boar, 126 
WiUiams, C. B., 21, 22, 104 
Wind, 27-30, 108 
Wind, affecting bird life, 111-112 
Woodpecker, 132 



Yuma, Arizona, 12, 31 

Z 

Zamenis, 130 

Zapus, 76, 79, 80 

Zarafshan, River, 55 

Zizera, 67 

Zizyphus, 55, 100, 111, 125, 137 

Zophosinse, 161 



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Messrs. Edward Arnold & Co/s 

AUTUMN 

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4 Edward Arnold dh Co.'s Autumn Announcements. 

accident, while bathing, which left him paralysed below the waist, 
with no hope of recovery. 

It was in these circumstances that he determined to devote what 
time and energy remained to him to the cause of Science, and for the 
rest of his life he worked with indomitable courage and brilhant 
success at intricate biological and biochemical problems, taking 
special interest in Mendehan research. The success was the more 
astonishing inasmuch as many of his investigations called for 
exceptional manual skill, which he acquired by dint of almost 
incredible perseverance, in spite of the fact that his hands and arms 
were still partially paralysed. In the summer of 1921 a list of his 
pubhshed scientific works was submitted to the Council of the Royal 
Society, in order that he might stand for election as a Fellow, but 
he died before attaining that distinction, on June 27th, 1922, leaving 
an example of high courage to which it would be hard to find a 
parallel. 

FROM CHINA TO HKAMTI LONG. 

By Captain F. KINGDON WARD, F.R.G.S. 

Author of " The Romance of Plant Hunting," " The Mystery Rivers 

OF Tibet," etc. 

One Volume. DemySvo. With Illustrations and Map. 18s.net. 

Captain Kingdon Ward has already made a reputation as one of 
the most intrepid explorers of the difficult and little-known country 
on the marches of Burma, China, and Tibet. The important journey 
described in this volume gives the reader an insight into the changes 
— physical, climatic, and botanical — which take place as the traveller 
passes westwards from the Yangtze across that narrow strip of 
earth's crust where the great rivers of South-East Asia escape from 
Tibet, and where jungle hides the head- waters of the mighty Irra- 
waddy. Captain Ward's primary object was to discover new plants, 
but to reach the wild districts which are his hunting-ground is no 
light task. Even to reach the city of Likiang in the heart of Asia 
involves a formidable journey, for there is no " Magic Carpet " to 
transport one thither. A glance at the Map which accompanies 
the book shows how formidable were the obstacles he had after- 
wards to surmount, at one moment bathed in tropical heat in the 
river valleys, at another wellnigh frozen on mountain ridges, 16,000 
feet above sea-level. Of great interest, apart from the difficulties 
of travel, are his accounts of the inhabitants and their manners and 
customs. Captain Ward possesses striking descriptive gifts and 
an admirable style ; he has the philosophy of a man who has spent 
much of his life in the vast open spaces of the world ; above all, he 
has the spirit of adventure. 



Edward Arnold dh Co.'s Autumn Announcements. 5 

RUSSIA AND RUSSIAN ART. 

By SIR W. MARTIN CONWAY, M.P. 

FORMEBLY SlADB PrOFESSOR OP FiNE ArTS IN THE UNIVERSITY OF CAM- 
BRIDGE. Author op " Palestine and Morocco," etc. 

One volume. Demy Svo. Illustrated. 16s. net. 

The present condition of Art in Russia has received little attention 
since the war, and Sir Martin Conway's visit this summer cannot 
fail to throw much new light upon an extremely interesting subject. 
Magnificent collections of pictures and priceless objects of Art 
formerly existed in Petrograd and Moscow, but how far they have 
suffered destruction or dispersal during the last few years is an open 
question. The result of Sir Martin Conway's inquiries will be 
extremely valuable to all students and lovers of Art in this country, 
and his shrewd and impartial observations on the general state of 
the country in 1924 will be especially welcome in view of the too 
often one-sided and interested glimpses which reach us from the 
interior of that darkened land. 

ADVENTURES OF CARL RYDELL. 

THE AUTOBIOGRAPHY OF A SEAFARING MAN. 

Edited by ELMER GREEN. 

One Volume. Demy Svo. With Illustrations and Map. 18s.net. 

This is a thrilling tale of adventure by a sailor of the old school, 
in various parts of the world. Carl Rydell is a Swede who began 
his remarkable career in the Swedish Navy. But being of an unruly 
disposition he soon got into trouble with the authorities, worked his 
way out to America and had a chequered career for many years, 
finally coming to anchor as Superintendent of the Nautical School 
in the Philippine Islands. *' I am not proud of some of my doings," 
he says, " but I have told the bad along with the good " ; and as few 
men can have seen more of the seamy side of a sailor's life, his narra- 
tive is extraordinarily interesting. In 1888 Rydell found himself in 
San Francisco, and it was on the Pacific coast that most of the follow- 
ing years were spent. That was the exciting period of the gold rush 
to Alaska, the period of sea-otter hunting and fur-seal " piracy," 
when bold men defied the law at the risk of their lives and were 
ready to suffer incredible hardships in their lust for gold. Many 
curious characters, the flotsam and jetsam of civilization, figure in 
these pages, and the whole book is one of those rare human docu- 
ments which a seafaring life occasionally creates for the enjoyment 
of the stay-at-home reader. 



6 Edward Arnold d; Co.'s Autumn Announcements. 

JORROCKS'S JAUNTS AND JOLLITIES. 

BEING THE HUNTING, SHOOTING. RACING, DRIVING, 
SAILING, EATING, ECCENTRIC AND EXTRAVAGANT 
EXPLOITS OF THAT RENOWNED SPORTING CITIZEN, 
MR. JOHN JORROCKS OF ST. BOTOLPH LANE AND 
GREAT CORAM STREET. 

By R. S. SURTEES, 

Author op "Handlhy Cross," "Mr. Sponge's Sporting Tour," btc. 

With 15 Coloured Plates after H. Aiken. Crown 4:to. 
21s.net. 

Robert Smith Surtees, the greatest hunting novelist of all time, 
whose biography has just been published sixty years after his death, 
has only recently begun to receive his due from the Uterary critics. 
Yet he is the man whose gift Thackeray once said he envied more 
than that of any man. And no wonder he did — for Surtees is the 
Dickens of the hunting field, and many of his odd characters are more 
ahve to-day than most of our flesh -and-blood acquaintances. Sur- 
tees is a national treasure, for he is one of the most peculiarly English 
writers of the last century. His pages are crowded with delight- 
fully drawn types, and of them all none is more beloved than the 
immortal John Jorrocks. It was the success of '* Jorrocks's Jaunts 
and Jollities," according to Mr. Thomas Seccombe in the Dictionary 
of National Biography, which led to the conception of a similar 
scheme which resulted in '* The Pickwick Papers." 

'* Tobe taken before * Handley Cross ' " is the author's recommen- 
dation in his preface to the second edition of this jolly book, in 
which are recorded the " eccentric and extravagant " exploits of 
Surtees' greatest character. And those people who have not 
already made the famous grocer-sportsman's acquaintance will do 
well to follow it and read of the earlier doings of the M.F.H. of 
Handley Cross. Those who are already devotees of this delectable 
story-teller will need no recommendation, beyond the fact that they 
have here for a reasonable price a handsome reproduction, including 
Aiken's famous coloured plates, of a work which in its earlier editions 
costs from fifty to a hundred pounds, according to the state of the 
copy purchased. 



Edward Arnold d; Co.'s Autumn Announcements. 7 

UNSCIENTIFIC ESSAYS. 

By F. WOOD JONES, M.B., D.Sc. 

Elder Professob op Anatomy in the University of Adelaide. AtrrHOR 
OP " Arboreal Man," etc. 

One Volume. Crown Svo. 6s. net. 
Professor Wood Jones is one of those men whose scientific attain- 
ments are combined with the possession of a charming Hterary 
style, and who, like Huxley, Drummond, and Fabre, have the art 
of writing round science in a way that the pubUc can understand and 
enjoy. The pages of this volume are the products of his idle 
moments, some of them passed in London, some in Austraha, and 
some upon a Coral Island in the Indian Ocean. The short essays 
have fascinating titles. Who would not envy the author his 
acquaintance with Fire-flies, with the Sea Serpent, with Wer 
Tigers ? The first chapter on *' Marvels " strikes the keynote of 
much that follows. Such essays as those on Evil Spirits, Moon- 
gazing, the Crab's Secret, Oily Patches, Sights and Scents, show how 
varied and uncommon is the menu presented to us. In others, less 
intriguing headings such as Coco-nuts, Seals and Sea Birds, Coral 
Islands and Clay Pans serve as pegs on which to hang a wealth of 
original thought and suggestion. And all through the book runs 
a strong vein of sentiment and romance which adds to the subtle 
spell the author weaves for our enchantment. 

ANTIQUES : 

THEIR RESTORATION AND PRESERVATION. 
By A. LUCAS, F.I.C., 

Chemist in the Department of Antiquities, Cairo. 
Crown Svo, 6s. net. 
The preservation of antiquities is one of the most difficult problems 
that confronts collectors and curators of Museums and Art Galleries. 
Mr. Lucas has written a practical account, devoid of technicahties, 
so that his accumulated knowledge may be readily available to 
those interested in the subject. His practical experience has 
extended over a number of years, and he has recently been 
associated with Mr. Howard Carter in regard to the preservation 
of the numerous art treasures found in the Tomb of Tutankamen. 
He commences with a general account of methods of preservation 
and restoration, emphasizing the necessity of a prehminary 
examination as to the nature and composition of the object before 
applying any specific treatment. This is followed by an account 
of the best methods available for use with the different materials 
such as papyrus, paintings, bronzes, etc. — ^the materials being 



8 Edward Arnold <fh Co.^s Autumn Announcements, 

arranged in alphabetical order. Finally, descriptions are given of 
certain simple physical and chemical tests which should be applied 
to the object in order to obtain information as to its composition, 
with a view to ascertaining the best method of preserving it. 
Detailed instructions are given for making up any solutions required 
in the course of the work. 

A HUNDRED YEARS IN THE HIGHLANDS. 

By OSGOOD MACKENZIE. 
New and Cheaper Edition. Crown 8fo. Illustrated. 
7s. 6d. net. 
The late Mr. Osgood Mackenzie's delightful collection of Highland 
lore and memories, including those of his uncle. Dr. John Macken- 
zie, has passed through several editions in its original form, and has 
been acclaimed as worthy to rank with such classics as Scrope, St. 
John, and Colquhoun. This new and cheaper edition will undoubt- 
edly be warmly welcomed by a large circle of readers for whom the 
price of the original work was somewhat high and will enable the 
possessor of the smallest library to add to it a work of the highest 
interest. *' To all those," said The Times, " who reverence ancient 
customs and lore of the West Coast Highlands, this book will be 
a real dehght." The Author loves the hills and the sea, the heather 
and the loch. He loves the people, their language and traditions ; 
he has even a soft place in his heart for their superstitions. All 
forms of Highland sport are familiar to him, and he possesses a keen 
and kindly sense of humour, which gives rise to many a well-told 
anecdote and permeates the whole book. 

ENGLISH LITERATURE BEFORE 
CHAUCER. 

By P. G. THOMAS, M.A., 

Reader in English Language and Literature in thb Untstbrsitt 

OF London. 

One Volume, Demy %vo. 8s. 6d. net. 

The time has gone by in which it was possible to speak of Chaucer 
as " the Father of English poetry." He will always remain one 
of its greatest masters, but investigation into the sources of English 
literature has brought to light materials many centuries older, and 
these not merely of antiquarian interest, but evidently the pro- 
ducts of an advanced civilization. 

In this book the author has set himself the task of giving within 
moderate compass and without excessive detail a reasoned serial 
recital of the examples we possess of Old and Middle English 



» 



Edward Arnold d; Co.^s Autumn Announcements. 9 

literature, and an illuminating exposition of their value and char- 
acteristics, both linguistic and literary, thus bringing into clear 
perspective the development of the various forms which served 
as the prototypes for later work. 

Not only will the book prove a useful introduction to the student 
preparatory to a more detailed study of individual texts, but the 
reader whose literary interests are more general, and to whom this 
period has been perhaps a terra incognita, will find much to attract him 
in the early examples of EngUsh epic poetry, romance, lyric, satire, 
and the short story, with whose later manifestations he is familiar. 

TRAGEDY. 

By W. MACNEILE DIXON, LL.B., Litt.D. 

Professob of English Language and Literature in the University 

OF Glasgow. 

Crown Svo. Probable price, 6s, net. 

Though the author of this Essay points out some features of the 
Athenian theatre which fatefuUy combined to favour the birth 
of Tragedy, he is not greatly concerned with any ordinary question 
of " origins," and holds simply that Tragedy burst from the brain 
of ^schylus like Athena from the head of Zeus, attaining at once 
its fullest imaginable stature. The justification of " the ways 
of God to Man," "the Problem of Evil," "the Riddle of the 
Universe " — in such phrases as these Professor Dixon's concep- 
tion of the scope of the Tragic theme are faintly adumbrated, 
and one is left wondering whether, without ^Eschylus' lead, even 
Sophocles would have compassed it fully ; of Euripides there is 
no question. Only once — with Shakespeare — was Tragedy reborn. 

The history of Tragedy is thus not a literary one ; it is to be 
sought rather in a way in which the world-philosophers, from Aris- 
totle to Hegel and Nietsche, have reacted to it. In the tracing of these 
reactions lies perhaps the principal interest of a stimulating book. 

NEW FICTION. 
MUCH DELUSION. 

By GERTRUDE SPINNY, 

Author of " The Painted Castle." 

Crown Svo. 7s. 6d. 

Miss Spinny's first novel, " The Painted Castle," won golden 

opinions from discerning critics who were quick to recognize qualities 

revealing unusual promise. In her new novel, the author has 

chosen a less difficult subject and one that will appeal more directly 



10 Edward Arnold dh Co.'s Autumn Announcements. 

to the experience of the reader. The story is Hghtly and amusingly 
told while developing a situation that becomes increasingly excit- 
ing. It begins quietly with the appearance of a stranger, Andrew 
Redman, who takes a furnished cottage in Sussex to recover from 
a nervous breakdown. He becomes acquainted with his neighbours, 
in particular with the Vicar, who is morbidly interested in Spiritual- 
ism, and with Miss Charlotte Masters, who Hves there with her grand- 
parents. Charlotte is regarded by the Vicar as a promising medium, 
and by Redman with eyes of love. Gradually the reader perceives 
that Redman is living under an assumed name, and learns that his 
breakdown was caused by circumstances not unconnected with the 
Vicar's mental disturbance. Redman's identity, when revealed, 
adds to the difficulty of his winning Charlotte. But a more terrible 
obstacle arises through the menacing attitude of the Vicar, whose 
delusions rapidly develop into mania and bring about a catastrophe 
in which Charlotte barely escapes a horrible death. The story is 
■carefully constructed and interesting from start to finish. 

THE PAPER MOON. 

By L. C. HOBART, 

^ Author op " The Silken Scarp." 

Crown 8vo. 7s. 6d. net. 

Miss Hobart's second novel is in every way stronger and more in- 
teresting than her first. The plot is weU constructed and developed 
with much emotional power. She has the gift of bringing her charac- 
ters and their setting vividly before the reader, and communicates 
the strong sympathy and antipathy she herself feels for them. 

The book opens amid idyllic surroundings on Dartmoor, but the 
scene soon shifts to a certain house in Chelsea, in outward appear- 
ance not different from its neighbours, but pregnant with some 
strange uncanny influence, some dimly apprehended evil lurking 
in the background, waiting for the moment of consummation. 
This malign atmosphere, the tense expectancy, the breathless 
suspense, Miss Hobart renders most vividly. 

The inhabitants of the house are Jonathan Fane and his son 
Greville ; from them also there seems to emanate a mysterious sug- 
gestion of hidden evil, of menace that may become reality. Greville 
is the villain of the story : he is a man who exercises irresistible 
iascination over the opposite sex, and first April Arless, then Rachel 
Strangways fall victims to his Mephistophelean attractions. In strong 
contrast with Greville is his cousin, Jake Fane, who is also in love 
with Rachel, and the characters of these two men typify the forces 
of good and evil which contend for mastery throughout the book. 



Edward Arnold <fc Co.'s Autumn Announcements. 11 

THE BIRTHMARK. 

By ALAN SULLIVAN. 
Crown 8vo. 7s. 6d. net. 

Mr. Sullivan's book is a sheer delight. Conceived in a spirit of 
satiric comedy, it is packed with witticisms that keep the reader 
chuckling happily to himself from the first page to the last. 

To Molding-on-the-Ooze, in " the lowest, flattest and dampest 
section of the Midlands," the seat of Henry Hardinger, Esq., come 
Colonel and Mrs. Bostwick, desiring its owner as a husband for 
their daughter Grace. Henry (who looks on life " as something 
between a polo match and a satiric comedy ") has no money 'f the 
Colonel has no money : each is ignorant of the other's want : each 
sees in Grace a solution of his difficulty. Every one takes a hand 
in the game of deceits, and as all concerned are both deceivers and 
deceived, the complications and the fun can be imagined. 

Mr. Sullivan is never at a loss : he *' keeps the ball rolling '* 
merrily. Unhesitatingly he puts his finger on the laughter-feedmg 
qualities in every one and every thing. He mocks, but it is with a 
kindly mockery that adds zest to life. 

As for the Birthmark — the part it plays in the game it would be 
unfair to reveal, but the comedy both above and below stairs makes 
joyous reading. To all who enjoy laughter we recommend this 
whimsical and witty book. 

SMITE THE ROCK. 

By OSWALD H. DAVIS, 

Author op " Soft Goods." 
Crown 8vo. 7s. 6d. net. 

All readers of Mr. Davis's brilUant first novel must have looked 
forward with eager interest to a second book from his pen. They 
will not be disappointed. 

" Smite the Rock " is, like " Soft Goods," a chronicle of the 
great Midland city of Ardencester, and is marked by the same 
sincerity and fineness of detail that distinguished the earher book. 
Life in a provincial city : the niceties of its class distinctions : its 
" high teas " : its chapel '* socials " : the ughness of its industrial- 
ism, are described with a vividness that is almost imcanny. 

Against these pettinesses of existence : these social differentia- 
tions : the drabness of the workers' hves : the things that " always 
have been and always will be," Frank Calder rebelled. The son 
of an employer and a capitalist, he ranges himself on the side of 



12 Edward Arnold db Co.'s Autumn Announcements. 

Labour, only to find his idealism shaken by contact with the indi- 
vidual representatives of the class he champions, and by the brute 
force of the mass. But the ideal of service, the purity of his con- 
ception, the instinct to fight for an idea, survive, and the book 
ends on a note of high hopefulness. 

Mr. Davis's subject is a fascinating one — ^the gradual development 
of a young man's character, his aspirations, his temptations — and 
he has handled it with masterly skill. 

A QUEST FOR A FORTUNE. 

" By PHILIPPA TYLER. 

Crown Sw. 7s. 6d. net. 

The scene of this interesting story is laid in Italy, land of romance 
and intrigue, which has so often attracted English novehsts and pro- 
vided them with exciting and entertaining plots. It was the happy 
hunting ground of Marion Crawford and of Richard Bagot, to mention 
only two favourite authors, and after reading Miss Tyler's work 
one wonders whether there is not some special deity who smiles 
upon the choice of that wonderful land as a field for fiction. Miss 
Tyler's novel has the atmosphere of Italy breathing through every 
page. We have the old aristocracy typified in the Prince di Consa 
and his beautiful daughters : like their magnificent palaces, glorious 
without, but faded and decaying within, the family presents to the 
world an appearance of stateliness and pride of race which hide 
ruined fortunes and an abandoned morale. The Prince himself 
carries off the situation boldly to the end, but the inevitable crash 
develops and wellnigh overwhelms his son Sigismondo, round whose 
efforts to restore the family fortunes the plot thickens. A good 
marriage is evidently the obvious solution, but what shall a young 
man do when love pulls one way and purse-strings another, not to 
speak of a very able and intriguing Marchesa di Pina who knows 
exactly what she wants and holds strong cards played with entire 
unscrupulousness. The Marchesa is a most original and effectively 
drawn character, and both Anita and Raffaella are such charming 
girls that it is hard to say which is the real heroine. We have pur- 
posely avoided unravelling the plot, which is extremely ingenious and 
well constructed and holds the reader's attention to the end. 

THE MIND OF MARK. 

By H. HERMAN CHILTON. 
Crovm 8vo. 7s. 6d. net. 
This is Mr. Chilton's first novel, and it is made noteworthy by 
his clever study of the character of his hero, Mark Rawson. The 



Edward Arnold d; Co.'s Autumn Announcements. 13 

author knows intimately the manners and conversation of the self- 
made Midland manufacturer and his associates, and his picture of 
Mark Rawson, so utterly absorbed in " getting on " — in " besting 
the other chaps " — that his home is, as it were, but a bye-product, 
has a photographic exactitude. 

As Mark's wealth had increased, so had his self-confidence and 
dominance. Once resolved on a course of action, he bends his 
Board of Directors to his will. When a strike occurs, he thinks 
to dominate his workpeople in like manner. But they are of less 
pliant material, and in the uproar Mark receives an injury to his 
head which brings on a long illness. 

For the first time in his life, he becomes an onlooker : he has 
leisure to think, and begins to readjust his values, to see that 
there is such a thing as compromise. 

But this new Mark Rawson is incomprehensible to his colleagues 
and — with the exception of his daughter Amy — to his family : 
he loses the support of the one and the sympathy of the other. 

The sincerity and power of the book are unmistakable, and the 
tragedy of the end is marked by a fine simplicity. 

A PASSAGE TO INDIA. 

By E. M. FORSTER, 

Author or " Howabds End," etc. 
7s. 6d. net. 

*^* Also a Collector's Large Paper Edition, limited to 200 copies, 

each copy signed by the Author, printed on Hand-made paper. 

Demy 8vo, price £2 25. net. 

Reviewed by Rose Macaulay in The Daily News : " Mr. E. M. Forster 
is to many people the most attractive and the most exquisite of contemporary 
novelists. . . . Never was a more convincing, a more pathetic, or a more 
amusing picture drawn of the Ruling Race in India. . . . 

"It is an ironic tragedy, but also a brilliant comedy of manners, and a 
delightful entertainment. Its passages of humour or beauty might, quoted, 
fill several columns." 

Reviewed by Sylvia Lynd in " Time and Tide " ; *' Reader, lo here, at 
last, a great book. There have been brilliant books in recent years, witty 
books, original books, books written in limpid and exquisite English ; but 
not imtil now has there been a book that was all these things. . . . 

" ' A Passage to India ' is a delicious and terrible book. ..." 

From The Spectator : " Of all the novels that have appeared in England 
this year, Mr. Forster's is probably the most considerable. . . . 

" ' A Passage to India ' is a disturbing, uncomfortable book. Its surface 
is so delicately and finely wrought that it pricks us at a thousand points. 
. . . The humour, irony, and satire that awake the attention and dehght 
the mind on every page all leave their sting." 



14 Edward Arnold d; Co.'s Autumn Announcements. 

Uniform Edition of 

Mr. E. M. Forster's Earlier Works. 

A new uniform edition can now be obtained of the following books. 
Bound in cloth, bs. net per volume. 

A ROOM WITH A VIEW. 

*• Mr. Forster's new novel clearly admits him to the limited class of writers 
who stand above and apart from the manufactm*ers of contemporary fiction." 
— Spectator. 

*' It is packed with wonderful impressions and radiant sayings." — Evening 
Standard. 

" We have originality and observation, and a book as clever as the other 
books that Mr. Forster has written already." — Times. 

THE LONGEST JOURNEY. 

" This novel is a very remarkable and distinguished piece of work. Its 
abundant cleverness fills even the more strenuous passages with vivacity. 
The strength of the book consists in its implicit indictment of the mean, 
conventional, self-deceitful insincerity of so much of modern EngHsh edu- 
cated middle-class life. This is certainly one of the cleverest and most 
original books that have appeared from a new writer since George Meredith 
first took the literary critics into his confidence." — Daily Telegraph. 

WHERE ANGELS FEAR TO TREAD. 

*' A remarkable book. Not often has the reviewer to welcome ''^a new 
writer and a new novel so directly conveying the impression of power and 
an easy mastery of material. Here there are quaUties of style and thought 
which awaken a sense of satisfaction and delight ; a taste in the selection 
of words ; a keen insight into the humour (and not merely the humours) 
of life ; and a challenge to its accepted courses. It is told with a deftness, 
a lightness, a grace of touch, and a radiant atmosphere of humour which 
mark a strength and capacity giving large promise for the future." — Daily 
News. 



HOWARDS END. 

Crown 8vo. 6s. net. A few copies still obtainable. 

" There is no doubt about it whatever. Mr. E. M. Forster is^one of the 
great novelists. All will agree as to the value of the book, as to'its absorb- 
ing interest, the art and power with which it is put together, and they will 
feel with us that it is a book quite out of the common by a writer who is 
one of our assets, and is likely to be one of our glories." — Daily JTelegraph. 



Edward Arnold d; Co.'s Autumn Announcements. 15 

RECENTLY PUBLISHED. 

MAN AND MYSTERY IN ASIA. 

By FERDINAND OSSENDOWSKI, 

Offiohsb d'Aoad6mie FiiANgAisE ; Authob of " Beasts, Men and Gods.'* 

With Map. Demy Svo. Third Impression. 14s. net. 

Morning Post. — " Every whit as enthralling as ' Beasts, Men and Gods.' '* 

Spectator. — " The most salient feature of Dr. Ossendowski's book is its 

revelation of the author's complex character. We are deeply impressed by 

his power of telling a story, for every chapter is not only interesting, it is 

exciting. One of the most exciting and vivid narratives we have ever read.'* 

THE ROMANCE OF PLANT HUNTING. 

By Captain F. KINGDON WARD, 

Author of " The Land of the Blue Poppy," etc. 

With Illustrations and Map. Demy Svo. 12s. 6d. net. 

Mr. Horace Hutchinson in The Queen. — " It is a book to be much com- 
mended to the expert and to the general reader alike." 

THE LAND OF THE SUN (QUEENSLAND). 

By E. J. BRADY, 

Author of '* Australia Unlimited," " The King's Caravan," etc. 
With Illustrations and Map. Crovm Svo. 7s. 6d. net. 

Liverpool Courier. — " Reads like a novel and sounds like a poem." 

LIFE AND ADVENTURE IN PEACE AND 

WAR. 

By Majoe-General Sir ELLIOTT WOOD, K.C.B. 
One Volume. With Portrait. Demy Svo. 16s. net. 

THE ASSAULT ON MOUNT EVEREST. 

By Brig.-General the Hon. C. G. BRUCE, 
And other Members of the Mount Everest Expedition. 

With 33 Full-page Illustrations and 2 Maps. Med. Svo. 

25s. net. 



16 Edward Arnold dh Co.'s Autumn Announcements. 

RECENTLY PUBLISHED. 

THE WANING OF THE MIDDLE AGES: 

A STUDY OF THE FORMS OF LIFE, THOUGHT AND ART 

IN FRANCE AND THE NETHERLANDS IN THE I4TH 

AND 15TH CENTURIES. 

By J. HUIZINGA, 

Pbofessok in the Univeesity of Leiden. 
With Illustrations. Demy Svo. 16s. net. 

" This thoughtful and well-ordered book, full of strange facts and shrewd 
comment, deserves careful study. The illustrations are delightful, and have 
evidently been selected with great care and judgment." — Times Literary 
Supplement. 

THE DISINHERITED FAMILY: 

A PLEA FOR FAMILY ENDOWMENT. 
By ELEANOR F. RATHBONE, M.A., J.R, CO., 

Author of " How the CAsuAii Laboureb Lives," etc. 

Croum Svo. 7s. 6d. net. 

Sir Wm. Beveridge in the Weekly Westminster. — " A remarkable book 
compact of vigorous argument and marshalled facts and wide personal ex- 
perience. It can be read by anybody and ought to be read by everybody." 

SUNSHINE AND OPEN AIR : 

THEIR INFLUENCE ON HEALTH. WITH SPECIAL 
REFERENCE TO THE ALPINE CLIMATE. 

By LEONARD HILL, M.B., F.R.S., 

Director Department of Applied Physiology, National Institute of 
Medical Research. 

Illustrated. Demy Svo. 10s. 6d. net. 

This book is well worth reading, and although of particular interest to 
the medical profession, should be much more widely appreciated. Both medi- 
cal and lay readers will find it full of interesting facts and permeated through- 
out with shrewd common sense." — The Lancet. 

CRIME AND INSANITY. 

By W. C. SULLIVAN, M.D., 

Medical Superintendent State Criminal Lunatic Asylum, Broadmoor. 
One Volume. Demy Svo. 12s. 6d. net. 

" We can thoroughly recommend this book to both jurists and medical 
men." — British Medical Journal. 

London : Edward Arnold & Co., 41 & 43 Maddox Street, W.l 






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